Update watchForNewFiles to allow reading already read files with a new timestamp

In TextIO and AvroIO, we have a configuration option called watchForNewFiles, and in FileIO.MatchConfiguration, we have an option called watchInterval. Right now, these match any files according to the filtering criteria, and then periodically check for new files. A file is determined to be new if it has a different filename than a file that has already been read.

We want to add an option to choose to consider a file new if it has a different timestamp from an existing file, even if the file itself has the same name.

See the following design doc for more detail:

https://docs.google.com/document/d/1xnacyLGNh6rbPGgTAh5D1gZVR8rHUBsMMRV3YkvlL08/edit?usp=sharing&resourcekey=0-be0uF-DdmwAz6Vg4Li9FNw