Apm system monitoring 7x

[cachedout]

This is a fix for the issue described here: elastic/apm-server#2708

This extends changes made here to the apm_system user: #40876

This is specifically made against the 7.x branch because in 8.0, we want to remove internal collectors for monitored services and so the configuration in the original bug report would not be supported. That said, I don't know if this is the preference of the Elasticsearch team and I defer to whatever they would like to do in that regard.

[cachedout]

@axw Can you confirm that this fixes the issue that you described in elastic/apm-server#2708

@jakelandis Could you please help me find the appropriate reviewers for this change on the Elasticsearch team?

[jakelandis]

This is specifically made against the 7.x branch because in 8.0, we want to remove internal collectors for monitored services and so the configuration in the original bug report would not be supported. That said, I don't know if this is the preference of the Elasticsearch team and I defer to whatever they would like to do in that regard.

@cachedout
Could you please introduce this to 8.0 and then backport to 7.x. Unless the conflicting change is already in master, it is preferred to add it and then remove it at the appropriate time.

[cachedout]

@jakelandis Will do. Thanks!

[axw]

@cachedout I've tested APM Server 7.2 with your ES branch, and it's working. Thanks!