[MNT] Change the "metric" parameter to "measure in the distance module

[chrisholder]

Reference Issues/PRs

#2379

What does this implement/fix? Explain your changes.

This PR changes the "metric" parameter to "measure" for the distance module. The reason for this is not all distance functions are metrics and therefore this parameter doesn't make sense for all distances.

Does your contribution introduce a new dependency? If yes, which one?

Any other comments?

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