[DOCS] Facilitates content re-use in the monitoring configuration

[lcawl]

Summary

This PR adds tagged regions to the following page in the Kibana Reference: https://www.elastic.co/guide/en/kibana/master/monitoring-metricbeat.html, so that the information can be re-used elsewhere.

It also clarifies that some steps pertain to the kibana-xpack module instead of the kibana module.

Finally, it expands the step related to configuring the kibana-xpack module so that it contains an example of the file's contents.

[skip ci]

Checklist

Use strikethroughs to remove checklist items you don't feel are applicable to this PR.

- [ ] This was checked for cross-browser compatibility, including a check against IE11
- [ ] Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support

• Documentation was added for features that require explanation or tutorials
  - [ ] Unit or functional tests were updated or added to match the most common scenarios
  - [ ] This was checked for keyboard-only and screenreader accessibility

For maintainers

• This was checked for breaking API changes and was labeled appropriately
• This includes a feature addition or change that requires a release note and was labeled appropriately

[elasticmachine]

Pinging @elastic/stack-monitoring

[elasticmachine]

Pinging @elastic/kibana-docs

[ycombinator]

The intent behind introducing the kibana-xpack module configuration variant in 7.2 was so users wouldn't need to manually edit the kibana module configuration file.

To that end, could we remove the configuration snippet shown in step 6 altogether? We'd still want to mention something about editing the host setting in modules.d/kibana-xpack.yml if they want to point to a Kibana instance other than the default at http://localhost:5601.

[cachedout]

This may be unrelated to this PR but I'll mention it anyway -- I have always sort of felt like the arrow between Kibana and Metricbeat is pointed in the wrong direction in the diagram on that page.

IMHO, an arrow that points from Kibana to Metricbeat suggests to me that it is Kibana which is responsible for sending data to Metricbeat when, in fact, it is Metricbeat which is responsible for pulling data from Kibana.

I think we should reverse the direction of the arrow at some point and rethink the visual layout of that diagram. I am happy to re-file this in a separate issue if that's best.

[lcawl]

I think we should ... rethink the visual layout of that diagram. I am happy to re-file this in a separate issue if that's best.

Thanks for the feedback @cachedout. If you can create an issue and offer suggestions, that would be great. From past experience, coming up with new diagrams will not something that can be quickly addressed as a side issue in this PR.

[lcawl]

To that end, could we remove the configuration snippet shown in step 6 altogether? ...

@ycombinator I've updated the description in step 6 to try to make it clearer that typically only the hosts, user, and password settings need to be changed. I rather like having the example in that step, however, since it might help people avoid the situation I encountered, where I was trying to enable both stats and status in the same file (albeit in an earlier version where this *-xpack.yml file didn't exist yet). If you still don't like it, however, let me know.

[ycombinator]

Thanks @lcawl, I like this less-imperative wording around the configuration.