oxide-auth's `RegisteredUrl::IgnorePortOnLocalhost` doesn't work when the host is 127.0.0.1 or [::1].
This commit lets the authentication process translate the host. The new registrar already supports this.
MSC2965 proposes to let the homeserver advertise its current OIDC authentication
issuer. These changes let conduwuit advertise itself as the issuer when
[global.auth.enable_oidc_login] is set. It also advertises its account management
endpoint if [global.auth.enable_oidc_account_management] is set.
None of these endpoints are implemented. This commit only implements the bare
advertisement, as requested by the MSC.
lafleur
Jade Ellis