SOLR-17439 Fix missing documentation for finding out non-standard PID for Solr in Docker

[rmueller83]

https://issues.apache.org/jira/browse/SOLR-17439

Description

The documentation misses a section for finding out a non-default PID.

Solution

Added a ps command for finding the PID.

Tests

I successfully executed the command in a running Solr 9.6.1 and 9.7.0 container.

Checklist

Please review the following and check all that apply:

• I have reviewed the guidelines for How to Contribute and my code conforms to the standards described there to the best of my ability.
• I have created a Jira issue and added the issue ID to my pull request title.
• I have given Solr maintainers access to contribute to my PR branch. (optional but recommended, not available for branches on forks living under an organisation)
• I have developed this patch against the main branch.
• I have run ./gradlew check.
• I have added tests for my changes.
• I have added documentation for the Reference Guide

[epugh]

I looked at this in context o fthe page, becasue at first I thought it was "too simple" and I agree it's a nice helper! Plus not everyone has years of java ops experience ;-)

[janhoy]

Hi, thanks for this. It's a tiny doc change, so normally we don't attribute it in CHANGES.txt and in release notes. However, we encourage you to keep contributing and for a more substantial change you'll for sure be mentioned :)

I'll back port this to 9x and 9.7 since our refguide docs can be fixed retroactively outside releases :)

[janhoy]

Realized too late that the PR was against branch_9_7. Normally we make changes to main first and then back port. This time I'll forward port to main...