roll in a opt-in flag for Soledad Client to opt-in into blobs
rationale:
- we want to be able to deploy blobs functionality in the server (capabilities) before the capability is feature-complete.
- we want to allow clients to opt-in for the blobs functionality before it's stable (to try out the feature, w/o working on mass migration of user data on an initial phase).
proposal:
blobs_enabled() = server_has_blobs() AND user_wants_blobs()
this is a flag that's only meaningful for the FIRST initialization of Soledad. After that, it should be saved into a json document.
question:
- should we override blobs=False if server_has_blobs=True and user_wants_blobs=False AND blobs=True found in capabilities document? I think we SHOULD.