[Enhancement] Support to configure the number of http worker threads on FE (backport #37530)

[mergify]

This is an automatic backport of pull request #37530 done by Mergify.
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Changes to be committed:
	modified:   fe/fe-core/src/main/java/com/starrocks/common/Config.java
	modified:   fe/fe-core/src/main/java/com/starrocks/http/HttpServer.java

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   docs/en/administration/FE_configuration.md
	deleted by us:   docs/zh/administration/FE_configuration.md

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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Why I'm doing: Http worker threads on FE are used to deal with http requests. Some requests may do heavy operations which will block threads, such as transaction stream load commit, and other operations that need to get lock. As a result, http server can't deal with other requests. Before optimizing these heavy operations, we first make the number of http worker threads to be configurable, and increase it as a candidate solution if the problem happens.

What I'm doing:
Add a configuration to adjust the number of http worker threads on FE

Fixes #issue

What type of PR is this:

• BugFix
• Feature
• Enhancement
• Refactor
• UT
• Doc
• Tool

Does this PR entail a change in behavior?

• Yes, this PR will result in a change in behavior.
• No, this PR will not result in a change in behavior.

If yes, please specify the type of change:

• Interface/UI changes: syntax, type conversion, expression evaluation, display information
• Parameter changes: default values, similar parameters but with different default values
• Policy changes: use new policy to replace old one, functionality automatically enabled
• Feature removed
• Miscellaneous: upgrade & downgrade compatibility, etc.

Checklist:

• I have added test cases for my bug fix or my new feature
• This pr needs user documentation (for new or modified features or behaviors)
  • I have added documentation for my new feature or new function
• This is a backport pr

[mergify]

@mergify[bot]: Backport conflict, please reslove the conflict and resubmit the pr

[sonarcloud]

Quality Gate failed

Failed conditions

C Maintainability Rating on New Code (required ≥ A)

See analysis details on SonarCloud

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