title: How to create/update multiple documents at once in Firestore
body: <p>Is it possible to store multiple documents in Firestore with only one request?
  With this loop it's possible but this would cause one save operation per item in the list.</p>
  
  <pre><code>for (counter in counters) {
      val counterDocRef = FirebaseFirestore.getInstance()
              .document("users/${auth.currentUser!!.uid}/lists/${listId}/counters/${counter.id}")
      val counterData = mapOf(
              "name" to counter.name,
              "score" to counter.score,
      )
      counterDocRef.set(counterData)
  }
  </code></pre>