Rename MatrixStatsAggregation.php to MaxAggregation.php

[mitelg]

cherry pick of this PR #313

we need the fix also for the 7.1.x version, because we are depending on Symfony 4.4 LTS

7.2 uses symfony/serializer ^5.0

[codecov-io]

Codecov Report

Merging #338 into 7.1 will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##                7.1     #338   +/-   ##
=========================================
  Coverage     78.59%   78.59%           
  Complexity      713      713           
=========================================
  Files           123      123           
  Lines          1887     1887           
=========================================
  Hits           1483     1483           
  Misses          404      404           

Impacted Files	Coverage Δ	Complexity Δ
src/Aggregation/Matrix/MaxAggregation.php	0.00% <ø> (ø)	10.00 <0.00> (?)

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[84m]

Thanks for your contribution @mitelg