[DOC] adds missing import statements in numba distance docstrings

[JonathanBechtel]

Reference Issues/PRs

Adds to #4264, also references #4324

What does this implement/fix? Explain your changes.

Distance calculation docstrings currently do not import the actual method from sktime, which makes it inconvenient to use the examples for quick use. This PR adds the import statement for each distance calculation in the docstring.

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

No

What should a reviewer concentrate their feedback on?

I would focus on the import statement added to each example, to make sure it matches the actual calculation being demonstrated

Did you add any tests for the change?

Since this is an update to a docstring I didn't add a test.

Any other comments?

None for now.

For all contributions

• [ x] I've added myself to the list of contributors.
• [x ] Optionally, I've updated sktime's CODEOWNERS to receive notifications about future changes to these files.
• [x ] The PR title starts with either [ENH], [MNT], [DOC], or [BUG] indicating whether the PR topic is related to enhancement, maintenance, documentation, or bug.

[fkiraly]

Thanks!

Still wondering how to test this...