Add matrix and analysis metadata standards (MAMS) file generation to SCXA

[pmb59]

To increase FAIRness, we need to consider adding a metadata scheme developed for single-cell analysis is matrix and metadata standards (MAMS) as a final part of the workflow, after tertiary analysis, for the AnnData file that we generate.

In practical terms, this consists in generating a file in JSON or YAML format. This file captures relevant information about the data matrices and annotations that are produced during analysis workflows for single-cell data, and could be part of the bundle that we distribute in the main resource page and/or the FTP. For that this R package can be used:
https://single-cell-mams.github.io/rmams/