Add RelativeAverageSpectralError and RootMeanSquaredErrorUsingSlidingWindow

[Piyush-97]

What does this PR do?

This PR adds a new metric Relative Average Spectral Error (RASE), and Root Mean Squared Error using Sliding Window the metric RASE is based upon.

Resolves part of #799

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• Was this discussed/approved via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?

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[codecov]

Codecov Report

Merging #816 (144fcac) into master (df15e09) will decrease coverage by 49%.
The diff coverage is 95%.

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #816     +/-   ##
========================================
- Coverage      88%     39%    -49%     
========================================
  Files         219     223      +4     
  Lines       11531   11672    +141     
========================================
- Hits        10189    4597   -5592     
- Misses       1342    7075   +5733     

[SkafteNicki]

Hi @Piyush-97, thanks for wanting to contribute.
However, I cannot see that you have made any changes. Is that correct?

[Piyush-97]

Hi @Piyush-97, thanks for wanting to contribute. However, I cannot see that you have made any changes. Is that correct?

Yes, Sorry about that I was busy with some other work and couldn't give mush time to this.
You can assign this to someone else if this need to be completed fast.
Sorry again.

[SkafteNicki]

Minor comments, else LGTM