Split extra libraries and add more granular control over tests

[Zeitsperre]

Overview

This Pull Request splits out the libraries that support some complex validators (geotiff, netcdf4, GDAL/OGR, zarr) so that basic data types are supported by default.

It also modifies some of the test controls so that pytest markers can be used to explicitly select/deselect tests that rely on these extra libraries.

Finally, coverage is now done across all builds in parallel, using tox-gh and the coverallsapp/github-action to remove the coveralls-python library.

Related Issue / Discussion

Changes here build on discussions found in #698

Closes #698

Additional Information

There are many more changes I'd like to implement, but I'll limit things here for now until discussion is had in #700.

Contribution Agreement

(as per https://github.com/geopython/pywps/blob/master/CONTRIBUTING.rst#contributions-and-licensing)

• I'd like to contribute [feature X|bugfix Y|docs|something else] to PyWPS. I confirm that my contributions to PyWPS will be compatible with the PyWPS license guidelines at the time of contribution.
• I have already previously agreed to the PyWPS Contributions and Licensing Guidelines

[coveralls]

coverage: 80.308% (-3.8%) from 84.104%
when pulling e633edc on extras-requirements
into 04f734b on main.

[Zeitsperre]

@cehbrecht I'm not certain why the coverage status is taking such a huge hit. I did remove a few useless imports, so it could be that the original values were too high?

[fmigneault]

@Zeitsperre
Potentially because the package were installed by default, their tests were running and checking some code paths (like their input format validation for example). Now, they would be skipped if not installed, therefore not "covered".