Adds select by gage id

Added

• New CLI option -g or --gage to support input of gage IDs instead of waterbody IDs.
• New function read_gage_ids() to parse gage IDs from input files or single inputs.
• New function get_wb_ids_from_gage_ids() to convert gage IDs to corresponding waterbody IDs.
• Support for CSV input files with a 'gage' or 'gage_id' column when using the -g option.
• Support for TXT input files with one gage ID per line when using the -g option.
• Support for single gage ID input directly via command line when using the -g option.

Changed

• Updated parse_arguments() function to include the new gage option.
• Modified validate_input() function to handle the new gage option and prevent simultaneous use of latlon and gage options.
• Updated main() function to process gage IDs when the -g option is specified.
• Expanded CLI documentation in the README to include information and examples for the new gage ID functionality.