feat: implement IndexOrderedSplitAssigner

[Meghajit]

As part of this issue, we want to add support for configuring a split assigner which can assign splits to source readers in an almost-deterministic order as decided by the user.

The order will be decided by the order of file paths specified as part of the StreamConfig SOURCE_PARQUET_FILE_PATHS.

[Meghajit]

Removing this from Support for Parquet Files as a Source Milestone as it is a nice to have for the first milestone
cc: @prakharmathur82