Simpler create endpoint

[joepio]

The /commit endpoint requires signing things. That is pretty hard to do without the @tomic/lib or atomic-lib libraries.

I'd like developers to be able to use a simpler endpoint. I think a /set endpoint could work. You can post JSON-AD resources there, and it will store the resources.

We have two approaches for storing:

• Commit based. The server converts the posted resource into a commit, by comparing to an existing resource, if it exists. The server signs the commit using the default_agent. Should it always delete unspecified properties?
• Overwrite based. Simply overwrite any existing resource with the new one. Simpler to implement, but no version data is stored, which makes the endpoint destructive.

Authentication

We need some form of authentication for this, at least if we allow it on publicly accessible servers.

Probably OIDC / OAuth Tokens #277