sgm-gharchive: add utility script (gharchive-find-missing-archives.py)

[halcyondude]

python gharchive-find-missing-archives.py --help                          
usage: gharchive-find-missing-archives.py [-h] [--years [YEARS ...]] [--start_date START_DATE] [--end_date END_DATE] [--persist]
                                          [--filename FILENAME] [--missing_files_list]
                                          directory
Check existence of hourly archive files in a specified directory.
positional arguments:
  directory             Directory path to check for files
options:
  -h, --help            show this help message and exit
  --years [YEARS ...]   Optional: Year(s) to check, e.g., 2023 or 2020 2021 2022
  --start_date START_DATE
                        Optional: Start date in YYYY-MM-DD format
  --end_date END_DATE   Optional: End date in YYYY-MM-DD format
  --persist             Optional: Persist data to file
  --filename FILENAME   Optional: Base filename for persisted data
  --missing_files_list  Optional: Create a list of missing files. Defaults to 'gha-missing-files.txt'
  --download_missing    Optional: Download missing files after analysis.