packetbeat/protos/tcp: add metrics for TCP header flags

[efd6]

Proposed commit message

See title.

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

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How to test this PR locally

Related issues

• Closes packetbeat: add metrics for TCP header flags #36992

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Build stats

• Start Time: 2023-11-07T21:54:21.784+0000

• Duration: 48 min 46 sec

Test stats 🧪

Test	Results
Failed	0
Passed	2361
Skipped	25
Total	2386

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[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b packetbeat_flag_metrics upstream/packetbeat_flag_metrics
git merge upstream/main
git push upstream packetbeat_flag_metrics