Updated metrics generator note

[ej25a]

Added a note that Metrics Generator can be enabled via Application Observability or to contact support for custom Metrics Generator configs. Mirrors the note found on this page for Metrics Generator https://grafana.com/docs/grafana-cloud/send-data/traces/metrics-generator/

Which issue(s) this PR fixes:
Fixes https://github.com/grafana/support-escalations/issues/12501

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

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[github-actions]

This PR must be merged before a backport PR will be created.

[knylander-grafana]

Greetings. Thank you for taking the time to submit a change to the docs. What prompted the update to focus on Application Observability within this note specifically?

I see that this is a copy of a note from the Cloud docs. The wording could be improved, but it brings up a larger issue. Does this note really belong in the Tempo docs or should we be directing people only to the Cloud Traces docs for setting up metrics-generator in the Cloud?

[knylander-grafana]

See my other comment. We should consider whether this is an appropriate update to the text in the Grafana Tempo docs. There may be another spot better suited to mentioning that metrics-generator is useful/required for Application Observability.

[knylander-grafana]

I read through the original issue linked in the description and found a few things:

• There are notes in the Tempo docs that were copied from the Cloud docs -- and should have remained only in the Cloud docs.
• Any information about configuration related to the Cloud Traces and metrics generator should be in the Cloud Traces docs and not in the Tempo docs.

I've corrected these things in this PR: #4151

If you feel that my PR meets the documentation needs for the support issue, my sugegstion is that we close this PR in favor of mine.

Thank you.

[knylander-grafana]

I'm going to close this PR in favor of this one: #4151

Please let me know if you feel that this other PR doesn't cover the content from the support issue.