Restore PAM user autocreation functionality (#15825) (#15867)

Backport #15825

* Restore PAM user autocreation functionality

PAM autoregistration of users currently fails due to email invalidity.
This PR adds a new setting to PAM to allow an email domain to be set
or just sets the email to the noreply address and if that fails falls
back to uuid@localhost

Fix #15702

Signed-off-by: Andrew Thornton <art27@cantab.net>

* As per KN4CKER

Signed-off-by: Andrew Thornton <art27@cantab.net>

Co-authored-by: 6543 <6543@obermui.de>

modules/forms/auth_form.go

@@ -51,6 +51,7 @@ type AuthenticationForm struct {
 	TLS                           bool
 	SkipVerify                    bool
 	PAMServiceName                string
+	PAMEmailDomain                string
 	Oauth2Provider                string
 	Oauth2Key                     string
 	Oauth2Secret                  string