- Introduce canonical reference rules via a payload entry in the identity

  document. The payload is identified by `xyz.radicle.crefs`, and the payload

  currently contains one key `rules`, which is followed by the set of rules. For

  each rule, there is a reference pattern string to identify the rule, which in

  turn is composed of the `allow` and `threshold` values. The canonical

  reference rules are now used to check for canonical updates. The rule for the

  `defaultBranch` of an `xyz.radicle.project` is synthesized from the identity

  document fields: `threshold` and `delegates`. This means that a rule for that

  reference is not allowed within the rule set. This checked when performing a

  `rad id update`.