Cherry-pick #22057 to 7.x: Add max_number_of_messages into aws filebeat fileset vars

[kaiyan-sheng]

Cherry-pick of PR #22057 to 7.x branch. Original message:

What does this PR do?

This PR is to add max_number_of_messages config parameter to each filebeat fileset under aws so this config can be used not only by the input itself, also with all the filesets.

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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Pinging @elastic/integrations-platforms (Team:Platforms)

[elasticmachine]

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Build stats

• Build Cause: [Pull request #22105 opened]

• Start Time: 2020-10-22T17:52:52.857+0000

• Duration: 74 min 5 sec

Test stats 🧪

Test	Results
Failed	0
Passed	1947
Skipped	259
Total	2206