[client] firebase as a client backend

[vsoch]

see https://code.tutsplus.com/tutorials/get-started-with-firebase-storage-for-ios--cms-30203

[vsoch]

For this hacktoberfest issue, you would need to:

• figure out where containers (or metadata) can be served in firebase
• add a client as a module folder under sregistry/main for firebase (use others as starter templates). Depending on what firebase can do, this determines the functions you provide (e.g., push, pull, inspect).
• add a documentation page!