feat(auth): add disable-2fa command (#38275)

This PR adds the `gitea admin user disable-2fa` command to disable 2FA
for a user

When the only admin in the instance loses their 2FA credentials, this
command can be used to disable 2FA, allowing them to log in and reset
it.

---------

Co-authored-by: Giteabot <teabot@gitea.io>

cmd/admin_user.go

@@ -18,6 +18,7 @@ func newUserCommand() *cli.Command {
 			microcmdUserDelete(),
 			newUserGenerateAccessTokenCommand(),
 			microcmdUserMustChangePassword(),
+			microcmdUserDisableTwoFactor(),
 		},
 	}
 }