Announce newrelic deployments deprecation

[hannahramadan]

The newrelic deployments command is being deprecated in the agent. We should add a warning to our docsite.

[github-actions]

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[PallaviWrite]

netlify build fork

[svc-docs-eng-opensource-bot]

✅ Your PR has been mirrored to our repository as PR #21847.
Commit: a3faa62a652f48bf2dca01ae24b64a73ac5ddf1a (a3faa62)
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[PallaviWrite]

lgtm