Fixes minimum observed cluster api level. Fixes api level check for vnodes. Adds more unit and integration tests for placement service.

[elena-kolevska]

Description

• Fixes minimum observed cluster API level. Previously, the raft state store didn't consider the minAPIlevel received as an argument on placement cluster startup. It was only considered when new dapr instances were trying to connect. This PR corrects that. (by @artursouza )
• Adds an integration test for the presence of vnodes in the placement table
• Moves and cleans up some reused placement service integration test code to the testing framework.

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly
• Created/updated tests
• Unit tests passing
• End-to-end tests passing

[codecov]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (48be4cd) 62.20% compared to head (d0be920) 62.15%.
Report is 1 commits behind head on master.

❗ Current head d0be920 differs from pull request most recent head 6d5e2d3. Consider uploading reports for the commit 6d5e2d3 to get more accurate results

Files	Patch %	Lines
pkg/placement/raft/server.go	0.00%	4 Missing ⚠️
pkg/placement/hashing/consistent_hash.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7462      +/-   ##
==========================================
- Coverage   62.20%   62.15%   -0.05%     
==========================================
  Files         244      244              
  Lines       22285    22292       +7     
==========================================
- Hits        13862    13856       -6     
- Misses       7275     7286      +11     
- Partials     1148     1150       +2     

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