Add custom routes to pages router (#7231)

* added custom routes

* fixed docs typos

* added page.customRoutes config validation

* added 404 response if missing custom route response

* added docs

* minor README formatting

* added CHANGELOG entry

* fixed bug in definitions builder that did not recognize array of custom type

* added missing route handler definition

* fixed custom routes definition

src/Config.js

@@ -168,6 +168,11 @@ export class Config {
     } else if (Object.prototype.toString.call(pages.customUrls) !== '[object Object]') {
       throw 'Parse Server option pages.customUrls must be an object.';
     }
+    if (pages.customRoutes === undefined) {
+      pages.customRoutes = PagesOptions.customRoutes.default;
+    } else if (!(pages.customRoutes instanceof Array)) {
+      throw 'Parse Server option pages.customRoutes must be an array.';
+    }
   }
 
   static validateIdempotencyOptions(idempotencyOptions) {