test(cubesql): Extract some join tests to separate module

[mcheshkov]

Check List

• Tests has 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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.67%. Comparing base (893004a) to head (c9d05fb).
Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #8777   +/-   ##
=======================================
  Coverage   82.67%   82.67%           
=======================================
  Files         217      218    +1     
  Lines       78125    78125           
=======================================
+ Hits        64588    64589    +1     
+ Misses      13537    13536    -1     

Flag	Coverage Δ
cubesql	82.67% <100.00%> (+<0.01%)	⬆️

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