fix(@angular-devkit/build-angular): add protractor as an optional peer dependency

protractor is currently used by the protractor builder within this package but is not represented in the dependencies. The can lead to accidental version mismatches as well as package manager hoisting problems due to the package manager not knowing the full dependency set of the package.

Author: clydin

packages/angular_devkit/build_angular/package.json

@@ -83,6 +83,7 @@
     "@angular/localize": "^11.0.0 || ^11.0.0-next",
     "karma": "^5.2.0",
     "ng-packagr": "^10.0.0",
+    "protractor": "^7.0.0",
     "typescript": ">=3.9 < 4.1"
   },
   "peerDependenciesMeta": {
@@ -94,6 +95,9 @@
     },
     "ng-packagr": {
       "optional": true
+    },
+    "protractor": {
+      "optional": true
     }
   }
 }