[CDAP-20758] Set max netty direct memory

[rmstar]

In Spark v3.2.0 and later, max netty direct memory must be >= max Spark remote block fetch size (ref).

So we set netty's max direct memory = remote block fetch size.
Spark remote block fetch size was set to a large value to address some issues with joins as part of CDAP-16461.

This fixes the following executor pod failure:

2023-08-03 16:19:37,019 - ERROR [dispatcher-Executor:o.a.s.i.Logging@98] - Executor self-exiting due to : Unable to create executor due to Netty direct memory should at least be bigger than 'spark.network.maxRemoteBlockSizeFetchToMem', but got 2075918336 bytes < 2147483135
org.apache.spark.SparkException: Netty direct memory should at least be bigger than 'spark.network.maxRemoteBlockSizeFetchToMem', but got 2075918336 bytes < 2147483135
	at org.apache.spark.executor.CoarseGrainedExecutorBackend.onStart(CoarseGrainedExecutorBackend.scala:96)

[albertshau]

would be good to reference the jira in case people want more context/info

It also seems like we should set it in the same place that spark.network.maxRemoteBlockSizeFetchToMem is being set. Otherwise if we ever change that value for some reason, this may break again.

[rmstar]

added reference to the jira. moved the code that sets io.netty.maxDirectMemory into the app where we set spark.network.maxRemoteBlockSizeFetchToMem