Hey, I would like to add the ability to choose the amount of reducers that can be used with the ShardedJoinStrategy. Currently, only the default number is chosen (500), this causes a lot of problems in my pipelines and will be a much slower alternative than using the DefaultJoinStrategy (for cases where I need around 5000 reducers). Due to the large data amount that needs to go through 500 reducers. I Have already opened a pull request a while ago, but I am willing to follow your structure and opening a JIRA ticket and then submit it according to the official process, if you guys think it is a good idea. I think this would increase the performance in crunch when using large data sets.
Basically this is what I want to add: https://github.com/apache/crunch/pull/8 --- Thanks! Joel Östlund
