[Fixes 12766] New fixes regarding the Timeseries API

[Gpetrak]

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This branch includes fixes in terms of the fields management through through the GET method of the endpoint: /api/v2/datasets//timeseries . Also the functionality of copying the time dimension (if exists) in a layer through the /copy was added.

[codecov]

Codecov Report

Attention: Patch coverage is 22.22222% with 14 lines in your changes missing coverage. Please review.

Project coverage is 67.96%. Comparing base (5eaad8a) to head (46a3b36).
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #12853      +/-   ##
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- Coverage   67.97%   67.96%   -0.02%     
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  Files         977      977              
  Lines       59040    59054      +14     
  Branches     6897     6899       +2     
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+ Hits        40132    40135       +3     
- Misses      17266    17275       +9     
- Partials     1642     1644       +2