Fix to_xarray kwargs for netcdf data object

[sandorkertesz]

Description

This PR:

• fixed the issue when the NetCDFData.to_xarray() method did not pass xarray_open_mfdataset_kwargs to the underlying reader.
• It also improved the docstring and tests of NetCDFData.to_xarray()

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 17.94872% with 32 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.29%. Comparing base (2a8a183) to head (510c6e9).

Files with missing lines	Patch %	Lines
tests/netcdf/test_netcdf_convert.py	17.94%	32 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1048      +/-   ##
==========================================
- Coverage   82.44%   82.29%   -0.16%     
==========================================
  Files         237      237              
  Lines       16757    16794      +37     
  Branches      818      818              
==========================================
+ Hits        13816    13821       +5     
- Misses       2698     2730      +32     
  Partials      243      243              

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