Add identifier field to AnnotatedChallenge subclasses (#10491)

This field is optional to maintain backwards compatibility. Note that
`AnnotatedChallenge` inherits from `jose.ImmutableMap`, which has a
[check in
__init__](https://github.com/certbot/josepy/blob/4b747476703fe4fff1aaccd76ebe570698bbf4f0/src/josepy/util.py#L125-L131)
that all slots are provided. That check would not allow us to do a
backwards-compatible addition, so I implemented an `__init__` for each
of these subclasses that fills the fields without calling the parent
`__init__`, and so doesn't hit an error when `identifier` is absent.

I chose to use `acme.messages.Identifier` rather than
`certbot._internal.san.SAN` here because these are wrapped ACME types,
so they should use the ACME representation. Also, `AnnotatedChallenge`
is passed to plugins, so we need to pass a type that the plugins can
understand.

Additionally, `domain` is marked as deprecated.

Part of #10346

/cc @bmw, who noticed the issue with `AnnotatedChallenge`
[here](https://github.com/certbot/certbot/pull/10468#issuecomment-3403294394)
and provided additional feedback
[here](https://github.com/jsha/certbot/pull/2#issuecomment-3534895793).
Note that there's still some work to do to finish excising `domain`
assumptions from this portion of the code.

---------

Co-authored-by: ohemorange <ebportnoy@gmail.com>

newsfragments/10491.changed

@@ -0,0 +1 @@
+`achallenges.KeyAuthorizationAnnotatedChallenge`, `achallenges.DNS`, and `achallenges.Other` have a new field `identifier`, of type `acme.messages.Identifier`. This should be used in place of the `domain` field, which is now deprecated both as an attribute and during object creation.