Loader: make the part appended to folder monitoring staging path configurable

[spenes]

Currently, folder monitoring staging files are always written to shredded folder under folder monitoring staging path. However, this folder name should be configurable instead of being hard-coded. Related line is in here.

Also, the path used with folder monitoring Snowflake stage during copy operation isn't configurable as well. It expects path of the stage to be exactly $given_folder_monitoring_staging_path/shredded. It should be configurable as well. Related line is in here.