feat: new relic NRQL search script

[robrap]

Description:

Updated the no-longer-needed new_relic_code_owner_audit.py to be a new new_relic_nrql_search.py script, which searches the NRQL in New Relic alert policies and dashboards for the provided regex. Use --help for details.

Also, added documentation for updating squad and theme names.

Merge checklist:

• [x] All reviewers approved
• [x] CI build is green
• [x] Changelog record added
• [x] Documentation updated (not only docstrings)
• [x] Commits are squashed

Merge checklist:

• [ ] update squad or theme name change runbook