Replace time_dim_mode with time_dims

[pawel-wolff]

Description

The Xarray engine kwarg time_dim_mode has been replaced with time_dims - an explicit list of time-related dimension role names.

Tests, examples and documentation have been adapted accordingly.

As an extra, a mechanism of ignoring a colliding dimension has been improved: if a dimension declared in the kwarg extra_dims collides with pre-defined dimensions, then it is silently ignored. A related paragraph in the documentation has been added, as well as relevant tests.

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 99.29577% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 81.26%. Comparing base (afa2ec6) to head (27421fd).

Files with missing lines	Patch %	Lines
tests/xr_engine/test_xr_engine_indexing.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #967      +/-   ##
===========================================
+ Coverage    81.08%   81.26%   +0.17%     
===========================================
  Files          222      223       +1     
  Lines        14489    14624     +135     
  Branches       718      718              
===========================================
+ Hits         11749    11884     +135     
  Misses        2521     2521              
  Partials       219      219              

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[sandorkertesz]

@pawel-wolff, thank your for this important development and for writing all the docs and tests.