update doc outline and extract how tos

[robrap]

Description:

docs: update published doc outline

Updates the doc index to provide some minor enhancements, and to include the monitoring decisions and how-tos.

See docs/monitoring/README.rst for the decision on how these docs were included.

Here is a screenshot of the new outline:

docs: refactor squad and theme name change how to

Extracts the following new how tos:

• search_new_relic_nrql.rst
• update_monitoring_for_squad_or_theme_changes.rst

Author concerns:

I'm uncertain about how I included the monitoring docs in the outline, but I didn't wanted to be blocked and I wanted to be able to point to these docs from the runbook.

Merge checklist:

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