[Canvas] Function usage telemetry

[crob611]

Summary

This adds a couple of buckets for functions in use that keys off a workpad's @timestamp field. This @timestamp field is updated on every workpad save, but we fire off a save when a workpad is loaded (if the user has write permission) so it should hopefully map closely to how recently the workpad was "viewed"

Also took the effort to write descriptions for each of our telemetry fields since that was recently made available.

[elasticmachine]

Pinging @elastic/kibana-presentation (Team:Presentation)

[crob611]

@elasticmachine merge upstream

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: f5d5840
• Storybooks Preview

Metrics [docs]

✅ unchanged

History

• 💔 Build #120965 failed d59c095

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@elasticmachine merge upstream

[clintandrewhall]

Looks really straightforward. Is there a way to flag or exclude demo workpads?

[crob611]

@clintandrewhall Nope, that's something we've talked about in the past that has been a hangup for our telemetry. At least with this strategy, it would only skew data if people are constantly viewing the demo workpads.

We've talked about adding a flag on the workpad schema to mark it as demo, but then we'd have to have some way to mark it as not a demo anymore if someone starts using it for real, but that's kind of hard to detect. So I think this is a good interim solution.

[kibanamachine]

💚 Backport successful

Status	Branch	Result
✅	7.x

This backport PR will be merged automatically after passing CI.