Update the configureCollectionBalancing documentation to explain that:

• If no per-collection chunkSize has ever been specified for a collection X, the global default chunk size is taken into account for balancing.
• If the command is invoked with chunkSize: 0 for a collection X, it resets the per-collection chunk size so that the balancer is relying again on the default chunk size for X.

This documentation change need to be applied for all versions greater or equal to v5.3.