Add "none" option to AveragePrecision

[SkafteNicki]

What does this PR do?

Fixes #1106
Docs state that average="none" is also an option for average precision metric, but currently it is not

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• Did you make sure to update the docs?
• Did you write any new necessary tests?

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[codecov]

Codecov Report

Merging #1116 (2ca577c) into master (d9c345b) will decrease coverage by 42%.
The diff coverage is 50%.

@@           Coverage Diff            @@
##           master   #1116     +/-   ##
========================================
- Coverage      94%     52%    -42%     
========================================
  Files         180     180             
  Lines        8079    8079             
========================================
- Hits         7594    4178   -3416     
- Misses        485    3901   +3416