feat(interactive): Refactor and fix some bugs for `AdminService`

[zhanglei1949]

In this PR, we refactor some of the Interactive AdminService and fix some bugs.

2. Limit the maximum number of bulk loading jobs via bulk_loading_job_count_.
3. Let all AdminActor APIs return seastar::future<gs::Result<seastar::sstring>>, with a mapping between gs::StatusCode and http status code, we can remove a lot of dummy code handling exception/unexpected behaviors.
4. Update the unit test for admin service.
5. Refine the returned HTTP code, previously we returns a generic 500 error regardless of the specific error encountered.

Fix #3515

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 27.76%. Comparing base (d46a354) to head (64eb44d). Report is 3 commits behind head on main.

:exclamation: Current head 64eb44d differs from pull request most recent head 5a02274. Consider uploading reports for the commit 5a02274 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3406   +/-   ##
=======================================
  Coverage   27.76%   27.76%           
=======================================
  Files         178      178           
  Lines       16245    16245           
=======================================
  Hits         4511     4511           
  Misses      11734    11734           

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[zhanglei1949]

This PR has been divided into several small, merged PRs into main.