chore: add plugin selection and fix encoding in gRPC example

[kartheek-hc]

Description

• The example under grpc is meant to serve plugins over both net/rpc and gRPC, however it is only supporting the GRPCPlugin since the plugin name is hardcoded
• The Python plugin implementation in the same example is writing bytes as is in the Put method and the file it creates looks like

  b'world'
  
  Written from plugin-python
  

Related Issue

N/A

How Has This Been Tested?

1. Verify that the netrpc based plugin works as expected

   $ KV_PROTO=netrpc KV_PLUGIN=./kv-go-netrpc ./kv put hello world
   2026-01-16T04:12:39.785+0530 [DEBUG] plugin: starting plugin: path=/bin/sh args=["sh", "-c", "./kv-go-netrpc"]
   2026-01-16T04:12:39.786+0530 [DEBUG] plugin: plugin started: path=/bin/sh pid=86840
   2026-01-16T04:12:39.786+0530 [DEBUG] plugin: waiting for RPC address: plugin=/bin/sh
   2026-01-16T04:12:39.834+0530 [DEBUG] plugin: using plugin: version=1
   2026-01-16T04:12:39.834+0530 [DEBUG] plugin.sh: plugin address: address=/var/folders/f0/3m5x22012pl_kcwgrv1xn16m0000gn/T/plugin1603026947 network=unix timestamp="2026-01-16T04:12:39.834+0530"
   2026-01-16T04:12:39.837+0530 [DEBUG] plugin.sh: 2026/01/16 04:12:39 [ERR] plugin: stream copy 'stderr' error: stream closed
   2026-01-16T04:12:39.837+0530 [DEBUG] plugin.sh: 2026/01/16 04:12:39 [DEBUG] plugin: plugin server: accept unix /var/folders/f0/3m5x22012pl_kcwgrv1xn16m0000gn/T/plugin1603026947: use of closed network connection
   2026-01-16T04:12:39.838+0530 [INFO]  plugin: plugin process exited: plugin=/bin/sh id=86840
   2026-01-16T04:12:39.838+0530 [DEBUG] plugin: plugin exited
   
   $ KV_PROTO=netrpc KV_PLUGIN=./kv-go-netrpc ./kv get hello
   2026-01-16T04:12:43.248+0530 [DEBUG] plugin: starting plugin: path=/bin/sh args=["sh", "-c", "./kv-go-netrpc"]
   2026-01-16T04:12:43.249+0530 [DEBUG] plugin: plugin started: path=/bin/sh pid=86951
   2026-01-16T04:12:43.249+0530 [DEBUG] plugin: waiting for RPC address: plugin=/bin/sh
   2026-01-16T04:12:43.278+0530 [DEBUG] plugin: using plugin: version=1
   2026-01-16T04:12:43.278+0530 [DEBUG] plugin.sh: plugin address: address=/var/folders/f0/3m5x22012pl_kcwgrv1xn16m0000gn/T/plugin3283603273 network=unix timestamp="2026-01-16T04:12:43.278+0530"
   world
   
   Written from plugin-go-netrpc
   2026-01-16T04:12:43.279+0530 [DEBUG] plugin.sh: 2026/01/16 04:12:43 [DEBUG] plugin: plugin server: accept unix /var/folders/f0/3m5x22012pl_kcwgrv1xn16m0000gn/T/plugin3283603273: use of closed network connection
   2026-01-16T04:12:43.279+0530 [INFO]  plugin: plugin process exited: plugin=/bin/sh id=86951
   2026-01-16T04:12:43.279+0530 [DEBUG] plugin: plugin exited
   

2. Verify the gRPC based Go plugin works as expected

   $ KV_PROTO=grpc KV_PLUGIN=./kv-go-grpc ./kv put hello world
   2026-01-16T04:14:04.277+0530 [DEBUG] plugin: starting plugin: path=/bin/sh args=["sh", "-c", "./kv-go-grpc"]
   2026-01-16T04:14:04.279+0530 [DEBUG] plugin: plugin started: path=/bin/sh pid=87786
   2026-01-16T04:14:04.279+0530 [DEBUG] plugin: waiting for RPC address: plugin=/bin/sh
   2026-01-16T04:14:05.703+0530 [DEBUG] plugin: using plugin: version=1
   2026-01-16T04:14:05.703+0530 [DEBUG] plugin.sh: plugin address: address=/var/folders/f0/3m5x22012pl_kcwgrv1xn16m0000gn/T/plugin937069144 network=unix timestamp="2026-01-16T04:14:05.702+0530"
   2026-01-16T04:14:05.704+0530 [TRACE] plugin.stdio: waiting for stdio data
   2026-01-16T04:14:05.706+0530 [DEBUG] plugin.stdio: received EOF, stopping recv loop: err="rpc error: code = Unavailable desc = error reading from server: EOF"
   2026-01-16T04:14:05.707+0530 [INFO]  plugin: plugin process exited: plugin=/bin/sh id=87786
   2026-01-16T04:14:05.707+0530 [DEBUG] plugin: plugin exited
   
   $ KV_PROTO=grpc KV_PLUGIN=./kv-go-grpc ./kv get hello
   2026-01-16T04:14:15.002+0530 [DEBUG] plugin: starting plugin: path=/bin/sh args=["sh", "-c", "./kv-go-grpc"]
   2026-01-16T04:14:15.004+0530 [DEBUG] plugin: plugin started: path=/bin/sh pid=87908
   2026-01-16T04:14:15.004+0530 [DEBUG] plugin: waiting for RPC address: plugin=/bin/sh
   2026-01-16T04:14:15.024+0530 [DEBUG] plugin: using plugin: version=1
   2026-01-16T04:14:15.024+0530 [DEBUG] plugin.sh: plugin address: address=/var/folders/f0/3m5x22012pl_kcwgrv1xn16m0000gn/T/plugin3694723558 network=unix timestamp="2026-01-16T04:14:15.024+0530"
   2026-01-16T04:14:15.025+0530 [TRACE] plugin.stdio: waiting for stdio data
   world
   
   Written from plugin-go-grpc
   2026-01-16T04:14:15.025+0530 [DEBUG] plugin.stdio: received EOF, stopping recv loop: err="rpc error: code = Unavailable desc = error reading from server: EOF"
   2026-01-16T04:14:15.026+0530 [INFO]  plugin: plugin process exited: plugin=/bin/sh id=87908
   2026-01-16T04:14:15.026+0530 [DEBUG] plugin: plugin exited
   

3. Verify the gRPC based Python plugin works as expected. Note the issue described in Error running python-plugin gRPC example #157 still exists

   $ KV_PROTO=grpc KV_PLUGIN="python plugin-python/plugin.py" ./kv put hello world
   2026-01-16T04:15:15.982+0530 [DEBUG] plugin: starting plugin: path=/bin/sh args=["sh", "-c", "python plugin-python/plugin.py"]
   2026-01-16T04:15:15.984+0530 [DEBUG] plugin: plugin started: path=/bin/sh pid=88553
   2026-01-16T04:15:15.984+0530 [DEBUG] plugin: waiting for RPC address: plugin=/bin/sh
   2026-01-16T04:15:16.110+0530 [DEBUG] plugin: using plugin: version=1
   2026-01-16T04:15:16.112+0530 [TRACE] plugin.stdio: waiting for stdio data
   2026-01-16T04:15:16.113+0530 [DEBUG] plugin.stdio: received EOF, stopping recv loop: err="rpc error: code = Unimplemented desc = Method not found!"
   2026-01-16T04:15:18.116+0530 [WARN]  plugin: plugin failed to exit gracefully
   2026-01-16T04:15:18.121+0530 [ERROR] plugin: plugin process exited: plugin=/bin/sh id=88553 error="signal: killed"
   
   $ KV_PROTO=grpc KV_PLUGIN="python plugin-python/plugin.py" ./kv get hello
   2026-01-16T04:15:24.418+0530 [DEBUG] plugin: starting plugin: path=/bin/sh args=["sh", "-c", "python plugin-python/plugin.py"]
   2026-01-16T04:15:24.420+0530 [DEBUG] plugin: plugin started: path=/bin/sh pid=88635
   2026-01-16T04:15:24.420+0530 [DEBUG] plugin: waiting for RPC address: plugin=/bin/sh
   2026-01-16T04:15:24.525+0530 [DEBUG] plugin: using plugin: version=1
   2026-01-16T04:15:24.526+0530 [TRACE] plugin.stdio: waiting for stdio data
   2026-01-16T04:15:24.526+0530 [DEBUG] plugin.stdio: received EOF, stopping recv loop: err="rpc error: code = Unimplemented desc = Method not found!"
   world
   
   Written from plugin-python
   2026-01-16T04:15:26.529+0530 [WARN]  plugin: plugin failed to exit gracefully
   2026-01-16T04:15:26.531+0530 [ERROR] plugin: plugin process exited: plugin=/bin/sh id=88635 error="signal: killed"