Feature/allow to set raw field metadata

[sandorkertesz]

Description

This PR allows using raw metadata keys in Field.set().

f1 = f.set({"metadata.level": 700, "metadata.typeOfLevel": "isobaricInhPa"}

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 81.57%. Comparing base (d81303d) to head (5917586).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1012      +/-   ##
===========================================
+ Coverage    81.38%   81.57%   +0.19%     
===========================================
  Files          236      236              
  Lines        15636    15803     +167     
  Branches       756      763       +7     
===========================================
+ Hits         12725    12892     +167     
  Misses        2686     2686              
  Partials       225      225              

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