WIP: Flink Session Mode

[thodson-usgs]

This PR would add a Bakery class for Flink's session mode, which could potentially allow a much more Dataflow-like user experience. But that's still a ways off...

pangeo-forge/pangeo-forge-cloud-federation#22

[thodson-usgs]

Session mode jobs are currently failing with:

Caused by: org.apache.flink.client.program.ProgramInvocationException: Neither a 'Main-Class', nor a 'program-class' entry was found in the jar file.
	at org.apache.flink.client.program.PackagedProgram.getEntryPointClassNameFromJar(PackagedProgram.java:437) ~[flink-dist-1.16.3.jar:1.16.3]
	at org.apache.flink.client.program.PackagedProgram.<init>(PackagedProgram.java:158) ~[flink-dist-1.16.3.jar:1.16.3]
	at org.apache.flink.client.program.PackagedProgram.<init>(PackagedProgram.java:65) ~[flink-dist-1.16.3.jar:1.16.3]
	at org.apache.flink.client.program.PackagedProgram$Builder.build(PackagedProgram.java:691) ~[flink-dist-1.16.3.jar:1.16.3]
	at org.apache.flink.runtime.webmonitor.handlers.utils.JarHandlerUtils$JarHandlerContext.toPackagedProgram(JarHandlerUtils.java:182) ~[flink-dist-1.16.3.jar:1.16.3]
	... 50 more