docs(observability): introduce observing ai workflows documentation

[MichaelDoyle]

This PR is the first in a series, attempting to alleviate a fairly broad set of current pain points with the telemetry docs. Here are a few of those:

• Streamline set-up of Firebase Genkit Monitoring by giving it a dedicated section in the docs
• Disambiguate Firebase Genkit (production) Monitoring from general observability features of the framework
• Prioritize firebase plugin over google-cloud plugin and generally alleviate confusion between the two
• Set up firebase plugin docs to "stand alone" i.e. do not delegate out to cloud plugin docs
• Refer to API docs as the source of truth for plugin configuration, instead focussing on use-cases
• Remove confusing and/or erroneous authentication documentation and assumptions
• Enable troubleshooting

Checklist (if applicable):

• PR title is following https://www.conventionalcommits.org/en/v1.0.0/
• [n/a] Tested (manually, unit tested, etc.)
• Docs updated (updated docs or a docs bug required)

[schnecle]

This is looking awesome!

[thedmail]

approved. editorial pass to follow.