Improved stability of Ratis addMemberToGroup and testThresholdSnapshot UT

[OneSizeFitsQuorum]

For addMemberToGroup UT:

• The previous UT operates the underlying state machine only after the leader is elected, and the state machine may not be fully restored at this time, thus making some subsequent judgments wrong. This PR changes to ensure that the Leader's state machine is not read until the leader is ready (i.e., the state machine is restored) to ensure that the CI environment does not fail

For testThresholdSnapshot UT:

• In CI environment, some threads are scheduled slowly, requiring 3 chances to generate Snapshot may lead to instability, so this PR is changed to 12 times, which is as low as possible in CI environment with weak resource environment

[HxpSerein]

LGTM

[sonarqubecloud]

Quality Gate passed

Kudos, no new issues were introduced!

0 New issues
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov-commenter]

Codecov Report

Attention: 10 lines in your changes are missing coverage. Please review.

Comparison is base (b57f320) 49.08% compared to head (3d205dc) 49.10%.
Report is 10 commits behind head on master.

Files	Patch %	Lines
...tdb/consensus/iot/logdispatcher/LogDispatcher.java	14.28%	6 Missing ⚠️
...a/org/apache/iotdb/consensus/iot/IoTConsensus.java	72.72%	3 Missing ⚠️
...he/iotdb/consensus/iot/IoTConsensusServerImpl.java	66.66%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #11717      +/-   ##
============================================
+ Coverage     49.08%   49.10%   +0.01%     
- Complexity    24977    25011      +34     
============================================
  Files          2817     2824       +7     
  Lines        176805   177023     +218     
  Branches      21200    21219      +19     
============================================
+ Hits          86781    86920     +139     
- Misses        90024    90103      +79     

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[SzyWilliam]

+1.
Mr. OneSizeFitsQuorum is the true master of code!