feat(linq): add possibility to generate Flux query without pivot() function

[bednar]

Closes #279

Proposed Changes

Add possibility to generate Flux query without pivot() function (LINQ).

Checklist

• CHANGELOG.md updated
• Rebased/mergeable
• A test has been added if appropriate
• dotnet test completes successfully
• Commit messages are in semantic format
• Sign CLA (if not already signed)

[codecov-commenter]

Codecov Report

Merging #291 (0739228) into master (85cf453) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #291   +/-   ##
=======================================
  Coverage   89.27%   89.28%           
=======================================
  Files          73       73           
  Lines        6238     6242    +4     
=======================================
+ Hits         5569     5573    +4     
  Misses        669      669           

Impacted Files	Coverage Δ
Client.Linq/InfluxDBQueryable.cs	86.74% <100.00%> (+0.32%)	⬆️
Client.Linq/Internal/QueryAggregator.cs	98.31% <100.00%> (+0.01%)	⬆️

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