Add option --skip-dir-with to skip directories containing a marker file

[ajclark]

This small PR adds new option --skip-dir-with=FILE to rsync, which allows skipping directories that contain a specified marker file. This is useful for selectively excluding directories from synchronization based on the presence of marker files rather than path patterns.

Implementation details

• Adds a new option --skip-dir-with=FILE that accepts a required filename parameter
• When the option is used, rsync will check each directory for the specified marker file
• If the marker file exists, the directory and all its contents are skipped during transfer