Allow $schema property in firebase.json (#6051)

* Allow $schema property in firebase.json

* Add $schema property via firebaseConfig.ts

---------

Co-authored-by: joehan <[email protected]>

Author: dominicbartl

schema/firebase-config.json

@@ -128,6 +128,10 @@
         }
     },
     "properties": {
+        "$schema": {
+            "format": "uri",
+            "type": "string"
+        },
         "database": {
             "anyOf": [
                 {

src/firebaseConfig.ts

@@ -234,6 +234,10 @@ export type EmulatorsConfig = {
 export type ExtensionsConfig = Record<string, string>;
 
 export type FirebaseConfig = {
+  /**
+   * @TJS-format uri
+   */
+  $schema?: string;
   database?: DatabaseConfig;
   firestore?: FirestoreConfig;
   functions?: FunctionsConfig;