This commit, mostly authored by @DaveCTurner,
adds documentation for elasticsearch-node tool #37696.
(cherry picked from commit 09425d5a5158c2d3fdad794411b3bbc4bba47b15)
* Adding new MonitoredSystem for APM server
* Teaching Monitoring template utils about APM server monitoring indices
* Documenting new monitoring index for APM server
* Adding monitoring index template for APM server
* Copy pasta typo
* Removing metrics.libbeat.config section from mapping
* Adding built-in user and role for APM server user
* Actually define the role :)
* Adding missing import
* Removing index template and system ID for apm server
* Shortening line lengths
* Updating expected number of built-in users in integration test
* Removing "system" from role and user names
* Rearranging users to make tests pass