docs(service-worker): fix the service-worker-getting-started docs example (#28020)

Changes:
- Change the project type to `service-worker`, so that it gets
  appropriate `package.json` (with `@angular/service-worker` dependency)
  and `angular.json` (with `serviceWorker: true` in production config).
- Move `ngsw-config.json` to the correct directory.
- Specify custom test commands for aio's `yarn example-e2e` to also
  verify that the ServiceWorker bits are set up correctly.

PR Close #28020

aio/content/examples/service-worker-getting-started/src/ngsw-config.json

@@ -1,25 +0,0 @@
-
-{
-  "index": "/index.html",
-  "assetGroups": [{
-    "name": "app",
-    "installMode": "prefetch",
-    "resources": {
-      "files": [
-        "/favicon.ico",
-        "/index.html",
-        "/*.css",
-        "/*.js"
-      ]
-    }
-  }, {
-    "name": "assets",
-    "installMode": "lazy",
-    "updateMode": "prefetch",
-    "resources": {
-      "files": [
-        "/assets/**"
-      ]
-    }
-  }]
-}