feat(cubesql): Add projection flattening rule

[mcheshkov]

Check List

• Tests have been run in packages where changes made if available
• Linter has been run for changed code
• Tests for the changes have been added if not covered yet
• Docs have been added / updated if required

Description of Changes Made (if issue reference is not provided)

Allow to flatten projection node into internal WrappedSelect. This should allow to execute plans like Projection(Filter(...)) as a single ungrouped wrapper with push-to-Cube

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.23%. Comparing base (9a73857) to head (62c6388).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9165      +/-   ##
==========================================
+ Coverage   83.17%   83.23%   +0.05%     
==========================================
  Files         226      226              
  Lines       80096    80372     +276     
==========================================
+ Hits        66620    66895     +275     
- Misses      13476    13477       +1     

Flag	Coverage Δ
cubesql	83.23% <100.00%> (+0.05%)	⬆️

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