Improve using aliases for wekeo-cds source and update docs and tests

[sandorkertesz]

Description

Makes the wekeocds source to deprecation explicit instead of inferred from the alias table.

This involves the following changes in ClassMaker:

• Alias inverted: ALIASES was {"wekeo-cds": "wekeocds"}, now {"wekeocds": "wekeo-cds"} — the dashed name is canonical and SOURCES is keyed by it.
• New DEPRECATED set: deprecation. A source can now be deprecated without being an alias.

2. Improved source alias testing

• These tests now rely the newly added SourceMaker._lookup() method to avoid using/modifying SourceMaker class variables (i.e. global resources)

3. Updated docs

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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.27%. Comparing base (03497a1) to head (25f9bb8).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1104      +/-   ##
===========================================
- Coverage    82.27%   82.27%   -0.01%     
===========================================
  Files          239      239              
  Lines        17025    17018       -7     
  Branches       823      823              
===========================================
- Hits         14007    14001       -6     
+ Misses        2771     2770       -1     
  Partials       247      247              

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