x-pack/filebeat/input/cel: add support for http+{unix,npipe} schemes

[efd6]

What does this PR do?

This adds support for requests to endpoints over Unix sockets and Windows named pipes using the https?+(unix|npipe) schemes. No testing at this stage since cel test infrastructure assumes a TCP transport.

It also marks the cel input as owned by SEI to avoid troubling agent-data-plane in the future.

Why is it important?

From #33571

This would be used connect to internal services that are only exposed locally. Services like Beats HTTP monitoring endpoint and Docker have APIs that listen on unix sockets. It would be useful if httpjson (and any future inputs that also monitor arbitrary HTTP services) could monitor data from these local APIs.

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

• Query inclusion in 8.6 backport for 8.6.1.

How to test this PR locally

Related issues

• Relates [Filebeat] Support unix sockets and named pipes in httpjson input #33571

Use cases

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Logs

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• Start Time: 2022-11-17T03:13:49.758+0000

• Duration: 73 min 5 sec

Test stats 🧪

Test	Results
Failed	0
Passed	2505
Skipped	167
Total	2672

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