Implement broadcast join optimization

[Dandandan]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
When we support broadcast exchanges #342 we can transform certain joins to utilize it.

Describe the solution you'd like

Currently all plans involving hash joins look like the following.

HashJoin <- RemoteExchange (partitioned) <- build side input
         <- RemoteExchange (partitioned) <- probe side input

When the build side is small (e.g. Spark uses 10MB * number of partitions for this by default - but generally bigger can help as well in my experience).

The new plan after optimization looks like this (note the missing exchange in the probe side, that side doesn't require shuffling now)

HashJoin <- BroadcastExchange <- build side input
         <- probe side input

Describe alternatives you've considered

Implement the (physical) optimization rule. The rule should run after the HashBuildProbeOrder rule from DataFusion.

Additional context