Add `identifier` fields, which will soon replace the `dnsName` fields,
to:
- `corepb.Authorization`
- `corepb.Order`
- `rapb.NewOrderRequest`
- `sapb.CountFQDNSetsRequest`
- `sapb.CountInvalidAuthorizationsRequest`
- `sapb.FQDNSetExistsRequest`
- `sapb.GetAuthorizationsRequest`
- `sapb.GetOrderForNamesRequest`
- `sapb.GetValidAuthorizationsRequest`
- `sapb.NewOrderRequest`
Populate these `identifier` fields in every function that creates
instances of these structs.
Use these `identifier` fields instead of `dnsName` fields (at least
preferentially) in every function that uses these structs. When crossing
component boundaries, don't assume they'll be present, for
deployability's sake.
Deployability note: Mismatched `cert-checker` and `sa` versions will be
incompatible because of a type change in the arguments to
`sa.SelectAuthzsMatchingIssuance`.
Part of #7311
3f879ed0b4