Fix apm agentcfg api key privileges

[carsonip]

Align with feature-roles.asciidoc

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[mergify]

This pull request does not have a backport label. Could you fix it @carsonip? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-/d./d is the label to automatically backport to the /d./d branch. /d is the digit
  NOTE: backport-skip has been added to this pull request.

[michel-laterman]

The "cluster": ["monitor"] permission is needed when using an API key as well to retrieve the cluster_uuid

[carsonip]

apm_writer privileges are outdated as well. They are for 7.x.

[endorama]

@carsonip I updated the file aligning it to permissions as being discussed in #4193

Is there anything else needed to move forward with this?

[carsonip]

I think you have everything covered. Do you want me to pull this out of draft and merge it, or to close this and let you handle everything in #4193?

[endorama]

@carsonip I would move forward and merge it, we didn't change this area in the other PR so I see little risk for conflicts.