global: find item revisions by holding

[mvesper]

• Adds find_by_holding to search for item revisions utilizing the stored holding informations.

[mvesper]

Certain usecases in invenio-circulation require the ability to search in old revisions of items.

This is a WIP PR to show one way, which would be utilizing postgres ability to search directly in JSON fields.

There seem to be some issues, though:

• Searching in JSON fields is likely going to be slow, since there is no index (JSONB could help)
• By using sqlalchemy_utils.types.JSONType certain niceties seem to be missing, which is why the current PR creates a plain SQL query.
• How much functionality do we need? Do we need date ranges and type casts? If yes, do we change JSONType and see to utilize SQLAlchemy or do we keep it the SQL statement way?

Let me hear your thoughts :)

[david-caro]

Looks good to me :)

[david-caro]

This looks good to me. About using the date in the tests, should not be a problem unless there's something really wrong on the host that runs the tests, so ok for me too.