Ensure that the default branch is only ever synthesized from the `Doc`'s
`threshold` and `delegates` value. If the rule is ever written into a `RawDoc`,
then the update of the that `RawDoc` must go through the `update::veryify`
function, which checks that the rule is not present.
The business logic of modifying the identity document should not live in the CLI
code for updating said document.
Instead, we extract out that logic into separate update functions and these are
using from the CLI instead.
Introduce the `rules` module beneath `canonical`. The implementation follows
the Canonical References RIP[^0].
A `Rule` defines the DIDs and threshold required to get the canonical tip
for a reference (or set of references). Since a `Rule` has some specific
validation rules, there can be two versions of a `Rule`. The `RawRule` is one
that can be easily constructed, serialized, and deserialized. It must then be
validated into a `ValidRule`, which validates any constraints, and can be used
in the computing of a canonical tip.
For convenience, a set of `ValidRule`s is wrapped into the `Rules` type, which
also has a further constraint that each rule refers to a specific `refspec`.
[0]: 1d1ce874f7
Lorenz Leutgeb
Fintan Halpenny