fix(service-worker): detect new version even if files are identical to an old one (#26006)

Previously, if an app version contained the same files as an older
version (e.g. making a change, then rolling it back), the SW would not
detect it as the latest version (and update clients).

This commit fixes it by adding a `timestamp` field in `ngsw.json`, which
makes each build unique (with sufficiently high probability).

Fixes #24338

PR Close #26006

packages/service-worker/config/src/generator.ts

@@ -32,6 +32,7 @@ export class Generator {
 
     return {
       configVersion: 1,
+      timestamp: Date.now(),
       appData: config.appData,
       index: joinUrls(this.baseHref, config.index), assetGroups,
       dataGroups: this.processDataGroups(config),