[BugFix] should acquire db lock out of createLoadTask to avoid dead lock (backport #55219)

[mergify]

Why I'm doing:

A dead lock issue is found:

Slow lock:

Thread "pool-21-thread-406" owns the database lock.
StreamLoadMgr.cleanSyncStreamLoadTasks() tries to acquire StreamLoadMgr.lock.writeLock() 0x00007fb9905311a8

Jstack:

Thread "thrift-server-pool-6208" owns the StreamLoadMgr.lock.writeLock(): 0x00007fb9905311a8 in StreamLoadMgr.beginLoadTask()

StreamLoadMgr.beginLoadTask() call StreamLoadMgr.createLoadTask() who is trying to acquire database lock

What I'm doing:

StreamLoadMgr.createLoadTask() don't acquire database lock.
StreamLoadMgr.beginLoadTask() first acquire database lock and unlock, then acquire StreamLoadMgr.lock.writeLock()

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.

[mergify]

Cherry-pick of 9af1024 has failed:

On branch mergify/bp/branch-3.3/pr-55219
Your branch is up to date with 'origin/branch-3.3'.

You are currently cherry-picking commit 9af1024b99.
  (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)

Changes to be committed:
	modified:   fe/fe-core/src/main/java/com/starrocks/load/routineload/RoutineLoadJob.java

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

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