Fix CP Group Name in CP Objects [API-2252]

[emreyigit]

The PR fixes wrong usage of CP groups. Before the introduced fix, the client was sending the CP group creation requests in wrong format. This was resulting that all CP objects created in default CP group. Now, it's fixed.

[Patras3]

LGTM, thanks for the fix.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 90.90909% with 1 line in your changes missing coverage. Please review.

Project coverage is 80.98%. Comparing base (a00048c) to head (0a8cc02).
Report is 12 commits behind head on master.

Files with missing lines	Patch %	Lines
src/Hazelcast.Net/CP/CPSubsystem.cs	90.90%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #913      +/-   ##
==========================================
- Coverage   81.07%   80.98%   -0.10%     
==========================================
  Files        1031     1031              
  Lines       25047    25047              
==========================================
- Hits        20307    20284      -23     
- Misses       4740     4763      +23     

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