title: Spring Firestore optimistic lock (data versioning)
body: <p>I'm looking for the way to enable Optimistic locking for Firestore DB document, but seems <code>@Version</code> annotation doesn't work.</p>
  <p>Currently I'm using <code>spring-cloud-gcp-starter-data-firestore</code> lib for extending <code>FirestoreReactiveRepository</code> interface repository. I've looked through the spring cloud gcp documentation and found nothing about optimistic locking and data versioning(using for example document's modificatioNumber field).</p>
  <p>My be someone knows are there any way to enable, declaratively (using some annotations) or programmatically, optimistic locking for Firestore DB documents using spring libs or some other libs?
  Thanks.</p>