fix(@angular-devkit/build-angular): add service-worker as optional peer dependency

The `@angular/service-worker` package is used by the browser and app-shell builders.
By adding the package as an optional peer dependency, package managers can ensure that the package is available to import.

Author: clydin

packages/angular_devkit/build_angular/package.json

@@ -81,6 +81,7 @@
   "peerDependencies": {
     "@angular/compiler-cli": "^11.0.0 || ^11.1.0-next",
     "@angular/localize": "^11.0.0 || ^11.1.0-next",
+    "@angular/service-worker": "^11.0.0 || ^11.1.0-next",
     "karma": "^5.2.0 || ^6.0.0",
     "ng-packagr": "^11.0.0 || ^11.1.0-next",
     "protractor": "^7.0.0",
@@ -91,6 +92,9 @@
     "@angular/localize": {
       "optional": true
     },
+    "@angular/service-worker": {
+      "optional": true
+    },
     "karma": {
       "optional": true
     },