Expose new joiner in replication status

[yuwmao]

New joiner can't vote and is excluded from quorum, so expose to upper layer to perceive this state.

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.

Project coverage is 66.16%. Comparing base (1a0cef8) to head (a21cae2).
Report is 142 commits behind head on master.

Files with missing lines	Patch %	Lines
src/lib/replication/repl_dev/raft_repl_dev.cpp	85.71%	0 Missing and 1 partial ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #655      +/-   ##
==========================================
+ Coverage   56.51%   66.16%   +9.64%     
==========================================
  Files         108      109       +1     
  Lines       10300    11257     +957     
  Branches     1402     1532     +130     
==========================================
+ Hits         5821     7448    +1627     
+ Misses       3894     3084     -810     
- Partials      585      725     +140     

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[JacksonYao287]

LGTM