Write reference documentation for OIDC API tokens

[indirect]

This should be a document in the Guides repo, named something like "OIDC API Key Reference", and can be based on the RFC reference-level explanation. It should explain:

• what is OIDC
• what is a provider, how do you view providers (presumably pointing towards /profile/oidc/providers)
• what do each of the properties for a provider mean? what values can they have? what does each value do? (issuer, jwks uri, response types, subject types, signing alg, scopes, claims)
• what is an API key role?
• what do each of the properties for an API key role mean? what values can they have? what does each value do? (scopes, valid for, gems, statement effect and principal and conditions)