Updating monitoring docs with direct monitoring configuration

[ycombinator]

Beats now have the ability to send their monitoring data directly to the monitoring Elasticsearch cluster (#9260). This PR updates the Beats monitoring documentation with this change.

Resolves #11637.

[elasticmachine]

Pinging @elastic/stack-monitoring

[lcawl]

I added a few minor updates to the X-Pack terminology and links. Hope that's okay!

[lcawl]

LGTM and builds successfully

[dedemorton]

LGTM, too!

[bmorelli25]

Follow up question on this PR. @lcawl, @dedemorton
Any reason why we removed xpack.monitoring.enabled from the documentation entirely, instead of marking it as deprecated?

[bmorelli25]

Also curious as to if the name "Xpack Monitoring" was purposefully left in the yml file?

https://github.com/elastic/beats/pull/11677/files#diff-0605d738822e1c7e296523bf9f4d20b1R1180

[dedemorton]

@ycombinator is probably the best person to answer @bmorelli25.

Incidentally, I'm running 7.0, and Kibana stops displaying Beats monitoring data if I remove xpack form this setting. Might be doing something wrong because I'm doing minimal setup to test privileges (not monitoring). The monitoring docs still need work....

[ycombinator]

Any reason why we removed xpack.monitoring.enabled from the documentation entirely, instead of marking it as deprecated?

I'm okay with leaving it and marking it as deprecated in the docs. I guess it depends on what our general policy around documenting deprecated settings is. @lcawl @dedemorton?

Also curious as to if the name "Xpack Monitoring" was purposefully left in the yml file?

This is an interesting one for sure. As this is a comment header in the yml file, I took it to mean the name of the feature, not necessarily strongly tied to the names of the settings under that header. Again, I'm open to changing this to just "Monitoring" too.

Incidentally, I'm running 7.0, and Kibana stops displaying Beats monitoring data if I remove xpack form this setting.

I commented on this here: #11329 (comment).