Modify behavior of Dynamic Destinations

The writeDynamic() method, implementing Dynamic Destinations writes files per destination per window per pane. 

This leads to an increase in the number of files generated.

The request is as follows:

A way to make it possible for the user to modify the behavior of Dynamic Destinations to control the number of output files being produced.

a.) We can consider adding user-configurable parameters like writers per bundle, increasing number of records processed per bundle

and/or

b.) Introduce a method implementing Dynamic Destinations but more dependent on the data passing through the pipeline, instead of windows/panes.

So instead of splitting every output file into roughly the number of destinations being written to, we let the user configure how output files should be divided across destinations.

Links:

[1] [https://beam.apache.org/releases/javadoc/2.19.0/index.html?org/apache/beam/sdk/io/FileIO.html](https://beam.apache.org/releases/javadoc/2.19.0/index.html?org/apache/beam/sdk/io/FileIO.html)

[2] [https://github.com/apache/beam/blob/da9e17288e8473925674a4691d9e86252e67d7d7/sdks/java/core/src/main/java/org/apache/beam/sdk/io/FileIO.java](https://github.com/apache/beam/blob/da9e17288e8473925674a4691d9e86252e67d7d7/sdks/java/core/src/main/java/org/apache/beam/sdk/io/FileIO.java)

Imported from Jira [BEAM-10068](https://issues.apache.org/jira/browse/BEAM-10068). Original Jira may contain additional context.
Reported by: mborkar.