[Filebeat] Add Cloudflare R2 to provider list

[legoguy1000]

What does this PR do?

Now that Cloudflare R2 is out of closed beta, this adds their domain to the provider list to automatically detect and set the provider field.

Why is it important?

Checklist

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

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[elasticmachine]

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• Start Time: 2022-08-08T13:07:37.447+0000

• Duration: 132 min 16 sec

Test stats :test_tube:

Test	Results
Failed	0
Passed	4346
Skipped	338
Total	4684

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[cmacknz]

/test

[elasticmachine]

Pinging @elastic/security-external-integrations (Team:Security-External Integrations)

[cmacknz]

The S3 input doesn't have a codeowner listed, and I see changes from both cloud monitoring and SEI in the history. Requesting review from those teams, and we should clarify who the codeowner for this module should be if we can.

[mergify[bot]]

This pull request does not have a backport label. If this is a bug or security fix, could you label this PR @legoguy1000? 🙏. For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change) To fixup this pull request, you need to add the backport labels for the needed branches, such as:
• backport-v8./d.0 is the label to automatically backport to the 8./d branch. /d is the digit

[legoguy1000]

Can this be merged?

[cmacknz]

Can someone from @elastic/obs-cloud-monitoring approve if they want to support this?