Error: 1466 - must not specify _key for this collection

[wajda]

This started happening on cluster deployments on attempts to insert data after #1048 fix. The error is apparently related to the dataSource collection although the error message isn't specific about it.

java.util.concurrent.CompletionException: com.arangodb.ArangoDBException: Response: 400, Error: 1466 - must not specify _key for this collection
	at java.base/java.util.concurrent.CompletableFuture.encodeRelay(CompletableFuture.java:367)
	at java.base/java.util.concurrent.CompletableFuture.completeRelay(CompletableFuture.java:376)
	at java.base/java.util.concurrent.CompletableFuture$UniRelay.tryFire(CompletableFuture.java:1019)
	at java.base/java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:506)
	at java.base/java.util.concurrent.CompletableFuture.completeExceptionally(CompletableFuture.java:2088)
	at com.arangodb.async.internal.velocystream.VstCommunicationAsync.lambda$execute$1(VstCommunicationAsync.java:101)
	at java.base/java.util.concurrent.CompletableFuture.uniWhenComplete(CompletableFuture.java:859)
	at java.base/java.util.concurrent.CompletableFuture$UniWhenComplete.tryFire(CompletableFuture.java:837)
	at java.base/java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:506)
	at java.base/java.util.concurrent.CompletableFuture.complete(CompletableFuture.java:2073)
	at com.arangodb.async.internal.velocystream.VstConnectionAsync.lambda$write$0(VstConnectionAsync.java:51)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
	at com.arangodb.internal.velocystream.internal.MessageStore.consume(MessageStore.java:62)
	at com.arangodb.internal.velocystream.internal.ChunkStore.checkCompleteness(ChunkStore.java:65)
	at com.arangodb.internal.velocystream.internal.ChunkStore.checkCompleteness(ChunkStore.java:59)
	at com.arangodb.internal.velocystream.internal.VstConnection.lambda$open$0(VstConnection.java:218)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
	at java.base/java.lang.Thread.run(Thread.java:829)
Caused by: com.arangodb.ArangoDBException: Response: 400, Error: 1466 - must not specify _key for this collection
	at com.arangodb.internal.util.ResponseUtils.checkError(ResponseUtils.java:55)
	at com.arangodb.internal.velocystream.VstCommunication.checkError(VstCommunication.java:157)
	at com.arangodb.async.internal.velocystream.VstCommunicationAsync.lambda$execute$1(VstCommunicationAsync.java:80)
	... 14 common frames omitted

fixes #1076