Added tileLevelMin/Max and colormap details to STAC xcube:data_vars

[edd3x]

[Description of PR]
Currently, our web visualisation development team have been using the /datasets endpoint from the xcube server API which provides tileLevelMin, tileLevelMax, colorBarName, colorBarMax and colorBarMin per data variable as part of the JSON output. We are however changing to ows.stac via the /ogc endpoint because it's faster, but the STAC JSON output does not provide the above-listed attributes.

What I have done here is to use the DatasetsContext to derive the tiling scheme and get the colormap details using derive_tiling_scheme() and get_color_mapping() in xcube/webapi/ows/stac/controllers.py so the xcube:data_vars in the STAC item JSON output will return the additional variables like tileLevelMin, tileLevelMax, colorBarName, colorBarMax and colorBarMin.

I created a new method _get_xc_data_variables and _get_xc_data_variable to return the xcube:data_vars.

Checklist:

• Add unit tests and/or doctests in docstrings
• Add docstrings and API docs for any new/modified user-facing classes and functions
• New/modified features documented in xcube/webapi/ows/stac/controllers.py
• Changes documented in CHANGES.md
• GitHub CI passes
• AppVeyor CI passes
• Test coverage remains or increases (target 100%)

[forman]

Hi @edd3x, thanks for the PR. The extension to data variables is very useful and code looks good!
In fact, we plan to deprecate the /datasets endpoint and use only STAC. Then, I'm sure we'll need to enrich the data variable object by even more information. To be compatible with such an extension, we might put the extra information into a dedicated object, either as an object in attrs or as new own property extra or similar. We'll let you know here asap. Stay tuned and thanks!

[forman]

Hey @edd3x, FYI, we haven't started the activity yet, but it is still on the roadmap for spring 2024.

[edd3x]

Hey @edd3x, FYI, we haven't started the activity yet, but it is still on the roadmap for spring 2024.

Thanks @forman for the update, looking forward to the release