feat(@schematics/angular): add guardType as an alias of implements in guard schematic

`implements` option will be removed in future in favor of `guardType`. This is because the implements guard pattern is deprecated in version 15.1

Author: alan-agius4

packages/schematics/angular/guard/schema.json

@@ -47,6 +47,7 @@
       "default": false
     },
     "implements": {
+      "alias": "guardType",
       "type": "array",
       "description": "Specifies which type of guard to create.",
       "uniqueItems": true,