Setting workerCacheMb to make its way to the WindmillStateCache Constructor

Setting --workerCacheMB seems to affect batch pipelines only. For Streaming, the cache seems to be hardcoded to 100Mb [1]. If possible, I would like to make it allowable to change the cache value in Streaming when setting -workerCacheMB.

I've never made changes to the Beam SDK, so I am super excited to work on this! 

[1] https://github.com/apache/beam/blob/5e659bb80bcbf70795f6806e05a255ee72706d9f/runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/WindmillStateCache.java#L73