Add relate parameter to Otsuthreshold

[bguetarni]

This is related to OtsuThreshold is missing the relate parameter #403.
Adds a relate parameter to be passed to image_filters.OtsuThreshold class.

Description

Added relate arguments in init, and call functional otsu_threshold with.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Documentation

Issues Fixed or Closed by This PR

• Fixes: #403.

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
  I just changed the function documentation.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[alessiamarcolini]

Thank you @bguetarni for this contribution 🙌

[alessiamarcolini]

@ernestoarbitrio the CI is not passing because openslide-python has been updated, I opened PR #416 to support the new version. When that is merged we can rebase this PR on master and then merge it

[codecov]

Codecov Report

Merging #415 (e33dbc7) into master (e33dbc7) will not change coverage.
The diff coverage is n/a.

❗ Current head e33dbc7 differs from pull request most recent head 7c0fcad. Consider uploading reports for the commit 7c0fcad to get more accurate results

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  Files           17        17           
  Lines         1433      1433           
  Branches       223       223           
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  Hits          1433      1433           

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