Self-hosted kbfs backend

Apologies if this is a duplicate feature request, I found no issues under the term “self hosted”.

What I would like is the ability to self-host my kbfs backend - for stuff I upload, using my own quota and my own server, so I don't have to rely on the “generosity” of a service like keybase.io providing me with “free 10GB” that may or may not disappear in the future.

I'm not sure how this would work internally - but I imagine it would be something along the lines of running my own “kbfsd” on the server in question and then somehow proving that it's mine (or at least, linking it to my config somehow). After this, files signed by me would be uploaded as some sort of reference to this server instead, so clients trying to access the file would request it from there instead.

No files or tests are named. Start by tracing the kbfs backend and client architecture, including the proposed kbfsd server and how files are referenced; done would mean a defined, working path for self-hosted storage, ownership or configuration linking, and client access.

Written by the indexing model from the issue text.