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

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