Wait for materialized value before completing in chunk upload

[mdedetrich]

About this change - What it does

Currently in Pekko we ignore the result when a chunk upload sink is uploaded, this PR fixes that.

Why this way

Originally when I wrote the kafkaBatchSink I wasn't that familiar with the graphDSL and in its original implementation I didn't pass in the successSink/failureGraph into the graph. What this meant is that while the core business logic would run, it wouldn't wait on completion of either the successSink or failureSink.

This may also help in the current flakiness of guardian tests.

Also make sure to hide whitespace when viewing the PR, also the PR requires a snapshot version of Pekko connectors due to needing this change apache/pekko-connectors#280

[mdedetrich]

This is the major difference which is that we pass in both the successSink and failureSink explicitly, this gives us access to the materialized values (explained below).

[mdedetrich]

Since we are passing in the sinks explicitly now, we have to supply an extra argument to GraphDSL.create that defines how to combine the materialization values of the sinks. In Pekko terminology, materialization is the result value of an activation of a sink (i.e. for a Kafka publisher sink, whenever the we push a value into the Kafka publisher then the materialized value is a result of that action which with the Kafka example would typically be a Future[NotUsed] or a Future[Done])

For this specific case of successSinkMat/failureSinkMat, they are both Future's that contain values we don't really care about. The only thing we do care about is if at least one of the Future's have failed and also that we only complete when both Future's are completed (this can be done asynchronously, hence the Future.sequence), we also we don't care about ordering.