Cherry-pick #18723 to 7.x: Avoid watching monitor logs

[michalpristas]

Cherry-pick of PR #18723 to 7.x branch. Original message:

What does this PR do?

This PR differentiates beat for its purpose (normal/monitoring) and avoids monitoring output of monitoring beats.
It does it checking special tags passed in descriptor if tag is present it redirect logs to {original_path}_monitor file/socket so it is not picked up by monitor

Why is it important?

to lower CPU consumption and avoid publishing monitoring logs about monitored logs

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

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Build stats

• Build Cause: [Pull request #18761 updated]

• Start Time: 2020-05-27T11:54:38.666+0000

• Duration: 33 min 26 sec