Cherry-pick #25128 to 7.x: [Filebeat] Add ZooKeeper Module

[jsoriano]

Cherry-pick of PR #25128 to 7.x branch. Original message:

What does this PR do?

Adds a new module for ZooKeeper logs.

Why is it important?

Requested by Elastic Cloud team to ingest ZooKeeper 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.

Author's Checklist

How to test this PR locally

cd beats/filebeat
TESTING_FILEBEAT_MODULES=zookeeper mage -v pythonIntegTest

Related issues

• Closes Filebeat module for zookeeper logs #25061

Use cases

Screenshots

Logs

[elasticmachine]

Pinging @elastic/integrations (Team:Integrations)

[elasticmachine]

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Build stats

• Build Cause: Pull request #25395 updated

• Start Time: 2021-04-29T09:36:46.577+0000

• Duration: 107 min 35 sec

• Commit: 9df487b

Test stats 🧪

Test	Results
Failed	0
Passed	13675
Skipped	2299
Total	15974

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Tests succeeded.

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Test stats 🧪

Test	Results
Failed	0
Passed	13675
Skipped	2299
Total	15974

[dedemorton]

You'll need this change to fix the broken doc build: #25402 (backport of #25401)