Add xarray Accessors for plotting CML paths

[cchwala]

Things done in this PR:

• [x] implement xarray Accessors for plotting CMLs
• [ ] (maybe also add xarray Accessor for distance calculation function)
• [x] make lower-level plotting function, which is called by the Accessor, more generic by not using xarray.Dataset or DataArray is input
• [x] update example notebook

Checklist:

• [x] contributes a first version of #28 , but some more discussion and adjusted implementation will be needed before it can be closed
• [x] Tests added and passed if fixing a bug or adding a new feature
• [x] All code checks from pre-commit passed
• [x] Added an entry in the CHANGELOG.md file

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (61c4063) to head (d78e368). Report is 9 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #29 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 3 4 +1 Lines 43 88 +45 ========================================= + Hits 43 88 +45 ```

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