MM-69311: Document new metric: mattermost_cluster_reliable_fallback_tcp

[agarciamontoro]

Summary

Document new metric: mattermost_cluster_reliable_fallback_tcp

The new metric will land on v11.9, and was cherry-picked to v11.7 and v11.8 as well. I still don't know what the docs policy is with regards to the releases. Should I change the target branch to be v11.9-documentation?

Ticket Link

https://mattermost.atlassian.net/browse/MM-69311

[github-actions]

Newest code from mattermost has been published to preview environment for Git SHA d04eadc

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 774807a5-2cfe-4932-a8db-fe622768771f

📥 Commits

Reviewing files that changed from the base of the PR and between 6e6ca68 and 769c214.

📒 Files selected for processing (1)

• source/administration-guide/scale/performance-monitoring-metrics.rst

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📝 Walkthrough

Walkthrough

A new documentation bullet was added for mattermost_cluster_reliable_fallback_tcp, describing it as a histogram for UDP SendBestEffort messages that fall back to TCP SendReliable when message size limits are exceeded, along with its bucket range and guidance text.

Changes

Cluster metrics documentation

Layer / File(s)	Summary
Add fallback metric entry source/administration-guide/scale/performance-monitoring-metrics.rst	Adds a new mattermost_cluster_reliable_fallback_tcp documentation bullet with its metric semantics, bucket range, and inline implementation reference.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely states the main change: documenting the new metric mattermost_cluster_reliable_fallback_tcp.
Description check	✅ Passed	The description is directly related to documenting the new metric and adds relevant release-branch context.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch MM-69311.new.metric

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_{Comment @coderabbitai help to get the list of available commands.}

[github-actions]

Newest code from mattermost has been published to preview environment for Git SHA 769c214