feat: add leader_status for RegionRoute

[WenyXu]

I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

We should downgrade a Region before deactivating it:

• During the Region Failover Procedure.
• Migrating a Region.

Notes: Meta Server will stop renewing the lease for the downgraded [Region].

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)

#2638

[codecov]

Codecov Report

Merging #2670 (8ce4b0a) into develop (d77003f) will decrease coverage by 0.40%.
The diff coverage is 94.33%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2670      +/-   ##
===========================================
- Coverage    85.04%   84.64%   -0.40%     
===========================================
  Files          740      740              
  Lines       120457   120510      +53     
===========================================
- Hits        102440   102008     -432     
- Misses       18017    18502     +485     

[fengjiachun]

LGTM