cffconvert causes conflicts with the latest JSON schema

[irm-codebase]

This issue was triggered by snakemake/snakemake#3299

The cffconvert dependency included in the template breaks snakemake compatibility with JSON schema 2020-12 (the latest one). That tool has not been updated in a while (and it may not be if CFF does not use any of the new features in JSON 2020-12).

This points towards moving all these documentation dependencies some place else.
Including the CFF file is still a good idea (it helps people cite the modules easily), but we should be careful on the amount of base dependencies we add going forward.

In combination with the documentation maintainability concerns raised by @sjpfenninger (here #1 (comment)), it is probably a better idea to check for existence of certain files during the integration test, and then use those to build documentation at https://clio.readthedocs.io/.