Helper functions for new segmentation domain

[SkafteNicki]

What does this PR do?

This PR introduces a number of helper functions that will be beneficial for defining segmentation metrics.
In particular the two functions:

• binary_erosion
• distance_transform

are translated version of the corresponding functions from scipy.
We may need to change the utils in the future when we actually use them in metrics.

Before submitting

• Was this discussed/agreed 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?

PR review

Anyone in the community is free to review the PR once the tests have passed.
If we didn't discuss your PR in Github issues there's a high chance it will not be merged.

Did you have fun?

Make sure you had fun coding 🙃

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📚 Documentation preview 📚: https://torchmetrics--2105.org.readthedocs.build/en/2105/

[codecov]

Codecov Report

Merging #2105 (081dae1) into master (b07b2a5) will decrease coverage by 54%.
Report is 1 commits behind head on master.
The diff coverage is 84%.

Additional details and impacted files

@@           Coverage Diff            @@
##           master   #2105     +/-   ##
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- Coverage      87%     32%    -54%     
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  Files         293     294      +1     
  Lines       16465   16627    +162     
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- Hits        14300    5399   -8901     
- Misses       2165   11228   +9063