services: implement file fetching from external storage

[ppanero]

• closes files (sciebo): add support to fetch files from links payload #408
• closes files (sciebo): make allowed external domains for file fetchning configurable #410

Now there will be two "workflows" to upload files:
a) if the payload does not contain a uri/sotrage_class==E it goes as before: init will create the file record (no object version nor file instance), Then requests to /content and /commit are needed from the user to get the file in.

b) if the payload does contain a uri/sotrage_class==E, the init creates an object version and a file instance, and triggers the task to do a set_content and commit. Those actions are forbiden by the user.

[ppanero]

.

[slint]

LGTM! I think we're almost there, just a couple of naming and placement things to avoid data/code migrations in the future.

[ppanero]

Things shelved for the future:

• files: clarify transfer object/factory responsabilities and calling order #420

[slint]

We have to redo everything...

One missing entrypoint and we're good to go 🚀

[slint]

shelve/comment: we have to remember to configure this in app-rdm (and ZenodoRDM)

[ppanero]

@slint

• Entry point added (tasks)
• Commits squashes
• Opened issues:
  • add permission generator to rdm-records external files: apply new permission generator invenio-rdm-records#1119
  • file storage class config external files: overwrite files rest storage class list invenio-app-rdm#1955