auth: Add auth_name attribute for non external auth backends.

This commit adds `name` attribute for the backends that do not
have them.

This is just a kind of prep commit in case if we want to use
`self.logger.xxxx()` in the future which is dependent on the
`name` attribute. But right now these logging calls aren't used
anywhere in those backends.

zproject/backends.py

@@ -303,6 +303,8 @@ class EmailAuthBackend(ZulipAuthMixin):
     Allows a user to sign in using an email/password pair.
     """
 
+    name = 'email'
+
     @rate_limit_auth
     def authenticate(self, request: Optional[HttpRequest]=None, *,
                      username: str, password: str,
@@ -398,6 +400,8 @@ class ZulipLDAPAuthBackendBase(ZulipAuthMixin, LDAPBackend):
     file makes the flow for LDAP authentication clear.
     """
 
+    name = "ldap"
+
     def __init__(self) -> None:
         # Used to initialize a fake LDAP directly for both manual
         # and automated testing in a development environment where
@@ -871,6 +875,8 @@ class DevAuthBackend(ZulipAuthMixin):
     """Allow logging in as any user without a password.  This is used for
     convenience when developing Zulip, and is disabled in production."""
 
+    name = 'dev'
+
     def authenticate(self, request: Optional[HttpRequest]=None, *,
                      dev_auth_username: str, realm: Realm,
                      return_data: Optional[Dict[str, Any]]=None) -> Optional[UserProfile]: