fly certs --json arg is ignored

[guillaumekh]

Description
fly certs add and fly certs setup ignore the --json argument.

To repro:

fly certs setup test.acme-corp.com --json 

Expected result:
JSON output

Actual result:

You are creating a certificate for test.acme-corp.com
We are using Let's Encrypt for this certificate.

You can direct traffic to your Fly application by adding records to your DNS provider.

Choose your DNS setup:
[...]

Reproduced on:

• macOS 15.7.2
• fly 0.4.3 (obtained from homebrew)