docs: Add deprecation notice to source map upload docs

[bmorelli25]

Summary

Adds a deprecation notice to the source map upload docs and points to the new APM integration upload docs. Most of the work here (like creating a new source map guide for the Kibana API) was done in previous PRs.

This will only be backported to 7.16 and 7.17 as changes for ≥8.0 are in #6927.

Related issues

Closes #6433.

[apmmachine]

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• Start Time: 2021-12-22T19:48:32.640+0000

• Duration: 44 min 17 sec

• Commit: b35a85a

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Test	Results
Failed	0
Passed	5616
Skipped	19
Total	5635

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