add elasticsearch.privileges.cluster support

[stuartnelson3]

What does this PR do?

add an optional elasticsearch.cluster property to the package manifest to define cluster privileges to be assigned to an api key

Why is it important?

APM server needs additional cluster privileges to access / on its elasticsearch output

Checklist

• I have added test packages to test/packages that prove my change is effective.
• I have added an entry in versions/N/changelog.yml.

Related issues

proposed in #224

[stuartnelson3]

@mtojek I interpreted this sentence:

Maybe it would be good enough to keep it in the package manifest?

to mean that I should make my changes in the top-level manifest.yml. If this is wrong let me know!

[elasticmachine]

💚 Build Succeeded

the below badges are clickable and redirect to their specific view in the CI or DOCS

Expand to view the summary

Build stats

• Start Time: 2021-10-14T12:11:34.174+0000

• Duration: 2 min 12 sec

• Commit: 57ca8b8

🤖 GitHub comments

To re-run your PR in the CI, just comment with:

• /test : Re-trigger the build.

[ruflin]

@joshdover Requested your review on this from a Fleet perspective to make sure it will work as expected in Kibana. Ideally we would have the Kibana PR already open in parallel.

[joshdover]

Thanks. I'm going to delegate this to @nchaulet since he's working on elastic/kibana#114686 already.

[stuartnelson3]

Based on the work being done in elastic/kibana#114945, are we ok with the nesting? @joshdover @nchaulet

[mtojek]

I noticed that these properties are more or less sorted in prioritized order, which means that "elasticsearch" as extension should be at the bottom.

[mtojek]

@stuartnelson3 this one is still not addressed

[nchaulet]

Looks good to me, I have a working PR with that for Kibana and the package registry and looks like it's working 👍

[mtojek]

This PR hasn't received all approvals and got merged. There is also an unaddressed comment.