Allow for interpolation in `rectify_dataset()`

[forman]

Enhanced spatial resampling in module xcube.core.resampling:

• Added optional keyword argument interpolation to rectify_dataset() with values "nearest", "linear", or "bilinear". "linear" interpolates between 3 and "bilinear" between 4 adjacent source pixels.
• Added optional keyword argument rectify_kwargs to resample_in_space(). If given, it is spread into keyword arguments passed to the internal rectify_dataset() delegation, if any.
• Deprecated unused keyword argument xy_var_names of function rectify_dataset().

Closes #955

Checklist:

• [x] Add unit tests and/or doctests in docstrings
• [x] Add docstrings and API docs for any new/modified user-facing classes and functions
• [ ] ~New/modified features documented in docs/source/*~ (dedicated PR #957)
• [x] Changes documented in CHANGES.md
• [x] GitHub CI passes
• [x] AppVeyor CI passes
• [x] Test coverage remains or increases (target 100%)

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 97.36842% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 93.22%. Comparing base (96f1851) to head (1b59f2d).

:exclamation: Current head 1b59f2d differs from pull request most recent head 4be34c4. Consider uploading reports for the commit 4be34c4 to get more accurate results

Files	Patch %	Lines
xcube/core/resampling/rectify.py	95.55%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #956 +/- ## ======================================= Coverage 93.22% 93.22% ======================================= Files 458 458 Lines 35847 35908 +61 ======================================= + Hits 33417 33476 +59 - Misses 2430 2432 +2 ```

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