feat: get metasrv clusterinfo

[fengjiachun]

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Refer to a related PR or issue link (optional)

As the title said, provide a way to get the metasrvs info:

1. Make that each Metasrv node registers candidate information upon startup, sets the key (__metasrv_election_candidates/{address}), and keeps it alive every 300 seconds. The key will be delete when no keep lease.
2. Let the cluster client can get this information via gRPC service

Checklist

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
• This PR does not require documentation updates.

[codecov]

Codecov Report

Attention: Patch coverage is 3.90244% with 197 lines in your changes are missing coverage. Please review.

Project coverage is 85.06%. Comparing base (02f806f) to head (4347804).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3696      +/-   ##
==========================================
- Coverage   85.57%   85.06%   -0.51%     
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  Files         957      963       +6     
  Lines      159226   160622    +1396     
==========================================
+ Hits       136258   136637     +379     
- Misses      22968    23985    +1017     

[tisonkun]

LGTM.