Add additional days when combining daily satellite data for preBUFR

[mingchen-NOAA]

Pull Request Summary

This PR adds additional days in the merged monthly file when running pb2nc_merge_altimeter.py.

Description

This PR enables merging extra days when combining daily satellite data into monthly datasets for preBUFR. The change is intended to improve convenience in forecast-day evaluation.

• Adds a new variable, 'EXTRA_DAYS' which must be defined in the USER-DEFINED SETTINGS to specify how many additional days are included in the monthly output.
• Introduces an option to define the input directory for daily satellite datasets, allowing data to be merged from locations other than WORKDIR.
• Renames output variables from 'lat' -> 'latitude' and 'lon' -> 'longitude' for consistency with AODN.
• Adds print statements to display the merged daily data files and their paths.

Issue(s) addressed

fixes #107

Commit Message

Add extra days when combining daily satellite data into monthly for preBUFR

Check list

• Branch is up to date with the authoritative repository (NOAA-EMC) develop branch.

Testing

• How were these changes tested?
  Run pb2nc_merge_altimeter.py on Orion or Hercules with modified WORKDIR
  The output merged data should be in WORKDIR/precesssatdata/altimeter_monthly