[BugFix] Fix incorrect connection state update when register/unregister conn (backport #48056)

[mergify]

Why I'm doing:

Connection state update is incorrect.

What I'm doing:

Currently we need to update a few maps and counters when register/unregister
connection from FE, we don't have some sync mechanism to protect this update,
which may cause incorrect connection state and prompt "connection reach limit"
unexpectly to user login. Add lock protection when register/unregister connection,
the performance should be ok, we have moved some heavy operations like cleaning
tmp table outside of lock, and the rest are just some simple map get/put operations.

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

Bugfix cherry-pick branch check:

• I have checked the version labels which the pr will be auto-backported to the target branch
  • 3.3
  • 3.2
  • 3.1
  • 3.0
  • 2.5

---

This is an automatic backport of pull request #48056 done by [Mergify](https://mergify.com). ## Why I'm doing: Connection state update is incorrect.

What I'm doing:

Currently we need to update a few maps and counters when register/unregister
connection from FE, we don't have some sync mechanism to protect this update,
which may cause incorrect connection state and prompt "connection reach limit"
unexpectly to user login. Add lock protection when register/unregister connection,
the performance should be ok, we have moved some heavy operations like cleaning
tmp table outside of lock, and the rest are just some simple map get/put operations.

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]

Cherry-pick of 4d1ea24 has failed:

On branch mergify/bp/branch-2.5/pr-48056
Your branch is up to date with 'origin/branch-2.5'.

You are currently cherry-picking commit 4d1ea245db.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   fe/fe-core/src/main/java/com/starrocks/qe/ConnectScheduler.java

no changes added to commit (use "git add" and/or "git commit -a")

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

[mergify]

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