replicate: use bearer token instead of did

[TheButlah]

The previous DID stuff in the replicate crates were unecessary and too application specific. Its more useful to use a general bearer token, and leave how to validate that token and what its contents are up to the application.

A did-signed authentication attestation could just be a base64 signed message, and use that as the bearer token.

[TheButlah]

Forcing merge due to lack of review.