Implements VirtualMeter on PvInverterCluster

[chpoulter]

Added VirtualMeter interface to PvInverterCluster. This allows to configure, if values are added to the sum. Otherwise you end up with doubled values, as the sum will take the cluster as a normal pvInverter.

Made MeterType on the way configurable ... maybe useful for something.

[codecov[bot]]

Codecov Report

:x: Patch coverage is 74.86950% with 337 lines in your changes missing coverage. Please review.

Additional details and impacted files

@@              Coverage Diff              @@
##             develop    #3085      +/-   ##
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+ Coverage      59.50%   59.85%   +0.36%     
+ Complexity       113      112       -1     
=============================================
  Files           2770     2788      +18     
  Lines         119632   121038    +1406     
  Branches        8914     9060     +146     
=============================================
+ Hits           71180    72441    +1261     
- Misses         45765    45885     +120     
- Partials        2687     2712      +25     

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[chpoulter]

I did not see further discussion, so I just added the interface and adopted sum calculation. Was this the solution, which you had in mind?