feat: store federation metadata in SQLite

[dalpasso]

Important: this PR uses the branch db-for-collections-storage as base. Leaving as draft until this branch is merged.

Add the extension defined in https://github.com/Open-EO/openeo-api/blob/master/extensions/federation/README.md and store it in SQLite database.

This is a preparatory change to extend the fields within the federation metadata in the STAC server (CS-SI/stac-fastapi-eodag#108).

[alambare]

I don't understand why do we need to add a federation column in the database.
For what I understood, it is purely an informational field. We should probably keep it in the content column.

[dalpasso]

I don't understand why do we need to add a federation column in the database. For what I understood, it is purely an informational field. We should probably keep it in the content column.

It's in a separate column to avoid federation metadata to be overwritten by subsequent upsert_collections() calls in the STAC Server.