implement contributions/count[/density]/groupBy/boundary endpoints

[tyrasd]

Description

• Adds /groupBy/boundary versions of the /contributions/count[/density] endpoints
• fix handling of (deprecated) simplefeaturetypes filter (13d9945)
  N.B. this feature was broken since at least version 1.6.0 for /users/groupBy/boundary and /elements/*/groupBy/boundary requests

Corresponding issue

Closes #217. See also #115.

todo

• write docs
• implement integration tests
• add to changelog
• test functionality thoroughly
• check if code coverage can be increased

Checklist

• My code follows the code-style rules, and I have checked on the static analyses
• I have commented my code
• I have written javadoc (required for public methods)
• I have added sufficient unit and API tests
• I have made corresponding changes to the documentation
• I have updated the CHANGELOG.md
• I have adjusted the examples in the check-ohsome-api script or created an issue in the corresponding repository. More Information here. -> https://gitlab.gistools.geog.uni-heidelberg.de/giscience/big-data/ohsome/helpers/check-ohsome-api/-/commit/5a5f7640f4ff0e44ff16f3880608899c4f91ff5d
  checked by @joker234

[joker234]

We should check if we can increase the code coverage for the new/touched code, see here: https://sonarcloud.io/component_measures?branch=PR-230&id=org.heigit.ohsome%3Aohsome-api&metric=new_coverage&view=list

[tyrasd]

We should check if we can increase the code coverage for the new/touched code, see here: https://sonarcloud.io/component_measures?branch=PR-230&id=org.heigit.ohsome%3Aohsome-api&metric=new_coverage&view=list

puh, not sure how much sense it would make to test the methods in the Description class. 🤷

for the executor class: yeah, some paths are actually not covered, but AFAICS this is a general issue throughout our code. Instead of adding gazillions of test cases, it would be more beneficial to consolidate the code to a) reduce the code duplications, b) make the code more easily maintainable and c) be able to unit-test for example the output building of csv/json/geojson in a more centralized way.