feat: add upgrade candidate region step

[WenyXu]

I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

Add upgrade candidate region step:
It upgrades a candidate region to a leader region with a retry; if all retry fails, it will rollback the metadata.

Behaviors:
Retry:

• If require_ready is true, but the candidate region returns ready is false.
• MailboxTimeout.

Abort:

• The candidate region doesn't exist.
• PusherNotFound, The datanode is unreachable.
• PushMessage, The receiver is dropped.
• MailboxReceiver, The sender is dropped without sending (impossible).
• UnexpectedInstructionReply (impossible).
• Invalid JSON (impossible).

Checklist

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.

Refer to a related PR or issue link (optional)

#2700

[codecov]

Codecov Report

Merging #2829 (42d9e67) into develop (781f242) will decrease coverage by 0.32%.
Report is 1 commits behind head on develop.
The diff coverage is 93.15%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2829      +/-   ##
===========================================
- Coverage    84.74%   84.42%   -0.32%     
===========================================
  Files          740      740              
  Lines       115767   116244     +477     
===========================================
+ Hits         98105    98141      +36     
- Misses       17662    18103     +441     

[fengjiachun]

Rest LGTM

[WenyXu]

@MichaelScofield PTAL

[WenyXu]

@MichaelScofield PTAL