[8.x](backport #40912) x-pack/filebeat/input/cel: make http functions always available

[mergify]

Proposed commit message

HTTP functions were previously conditional on the resource URL being an HTTP/HTTPS URL. In hindsight, this offers no benefits and can result in confusing errors when the end user enters an invalid URL for an HTTP-based integration. Instead of a URL-related or HTTP-related error, the user is given a compilation error indicating that the HTTP-related function that are being called (and they may not be aware of in any way) are not valid references. So let's just always make them available.

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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This is an automatic backport of pull request #40912 done by [Mergify](https://mergify.com).

[botelastic]

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[mergify]

This pull request has not been merged yet. Could you please review and merge it @efd6? 🙏

[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 mergify/bp/8.x/pr-40912 upstream/mergify/bp/8.x/pr-40912
git merge upstream/8.x
git push upstream mergify/bp/8.x/pr-40912