saml: Add setting to skip the "continue to registration" page.

It's a smoother Just-In-Time provisioning process to allow
creating the account and getting signed in on the first login by the
user.

zproject/prod_settings_template.py

@@ -438,6 +438,12 @@ SOCIAL_AUTH_SAML_ENABLED_IDPS: Dict[str, Any] = {
         ## You can also limit subdomains by setting "attr_org_membership"
         ## to be a SAML attribute containing the allowed subdomains for a user.
         # "attr_org_membership": "member",
+        ##
+        ## Determines whether "Log in with SAML" will automatically
+        ## register a new account if one does not already exist. By
+        ## default, Zulip asks the user whether they want to create an
+        ## account or try to log in again using another method.
+        # "auto_signup": False,
     },
 }