feat: use constraints for queryables

[jlahovnik]

• queryables are created based on constraints if constraints_file_url is given for a provider (currently only implemented for cop_ads/cop_cds, wekeo can be done as soon as it is updated to the new endpoint)
• possible values are added to the queryables (if available)
• queryable parameters can be added to the request, to get only values matching the given condition for other queryables

[github-actions]

Test Results

    4 files  ± 0      4 suites  ±0   4m 38s ⏱️ -1s
  462 tests + 5    459 ✅ + 5   3 💤 ±0  0 ❌ ±0 
1 848 runs  +20  1 766 ✅ +18  82 💤 +2  0 ❌ ±0 

Results for commit 11b12d0. ± Comparison against base commit 3323b91.

♻️ This comment has been updated with latest results.

[github-actions]

Code Coverage (Ubuntu)

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Minimum allowed coverage is 70%

Generated by 🐒 cobertura-action against 88a3f2e

[github-actions]

Code Coverage (Windows)

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All files	76%	✅

Minimum allowed coverage is 70%

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[sbrunato]

Please:

• add a value attribute (from providers.yml default or given value) for returned queryables
  • this value should also be returned by lib methods, instead of actual default value
• pre-filter queryables available values using default values
• In datetime description, tell to refer to year, month, day contraints, if available
• return ids and not id
• return collections and not collection
• return geometry and not bbox
• add schema for geometry

[jlahovnik]

all change requests should be resolved

[jlahovnik]

all change requests implemented

[jlahovnik]

branch rebased

[sbrunato]

• when a parameter has a default value pre-configured, other available values are not listed, for example, on
  http://127.0.0.1:5000/collections/ERA5_SL/queryables?provider=cop_cds
  for api_product_type, we only reanalysis is listed, other values are missing
• also we may be able to override defaults with given additional filters (giving an empty value, or None in library mode), in order to be able to list all combinations

[jlahovnik]

• when a parameter has a default value pre-configured, other available values are not listed, for example, on
  http://127.0.0.1:5000/collections/ERA5_SL/queryables?provider=cop_cds
  for api_product_type, we only reanalysis is listed, other values are missing

  • also we may be able to override defaults with given additional filters (giving an empty value, or None in library mode), in order to be able to list all combinations

Defaults can now be removed by setting them to empty in the query params. In that case all the values of the parameter are no and no filtering by this parameter is applied.
About the first point: I kept this as it is for the moment because I think it might be confusing if we show all the values but the remaining parameters are filtered by one value. If the same constraints apply for several values, they are all shown.