feat(server): add flag to disable new sign ups (#6752)

packages/backend/server/src/fundamentals/config/def.ts

@@ -214,6 +214,8 @@ export interface AFFiNEConfig {
    * authentication config
    */
   auth: {
+    allowSignup: boolean;
+
     /**
      * The minimum and maximum length of the password when registering new users
      *

packages/backend/server/src/fundamentals/config/default.ts

@@ -147,6 +147,7 @@ export const getDefaultAFFiNEConfig: () => AFFiNEConfig = () => {
       playground: true,
     },
     auth: {
+      allowSignup: true,
       password: {
         minLength: node.prod ? 8 : 1,
         maxLength: 32,