Feature: WebSphere PMI subcollections support for connection pool metrics

[deejgregor]

This is a draft PR that I experimented with over the weekend to add support for WebSphere PMI subCollections support so that connection pool metrics could be retrieved. I would be interesting in discussing the possibility of adding this to jmxfetch.

WebSphere connection pool statistics (type:JDBCProvider) are little tricky to gather over JMX because the statistics are exposed using a non-standard subCollections method on a non-standard StatsImpl object (docs) and the sub-collection objects use non-standard statistics value objects (com.ibm.ws.pmi.stat.CountStatisticImpl, etc.). This PR adds support for both (1) the non-standard attribute objects in PmiSubCollectionAttribute, following the existing pattern and reusing code from JmxTabularAttribute and (2) statistics objects in PmiStatisticsAttributes, mirroring the patterns in JeeStatisticsAttributes.

[dd.trace 2025-11-12 02:12:14:048 +0000] [dd-jmx-collector] INFO datadog.communication.monitor.LoggingStatsDClient - websphere.jdbc_provider.use_time.total_ms:3|c|#subcollection:default/ds,instance:dd-java-agent for websphere,jmx_domain:WebSphere,dd.internal.jmx_check_name:jmxfetch-websphere-config,node:DefaultNode01,process:server1,Server:server1,J2EEServer:server1,mbeanIdentifier:cells/DefaultCell01/nodes/DefaultNode01/servers/server1/resources.xml#JDBCProvider_1762912381235,j2eeType:JDBCResource,name:Oracle JDBC Driver (XA),type:JDBCProvider,cell:DefaultCell01,version:9.0.5.24,platform:dynamicproxy,spec:1.0,runtime-id:9314ec31-8e12-4392-b193-c573950e3dbe,service:com.ibm.wsspi.bootstrap.WSPreLauncher

You can see the configuration for this here: deejgregor/dd-trace-java@a8d6cb7

And here is a docker compose setup to test this: https://github.com/deejgregor/websphere-setup/tree/feature-pmi-subcollections