Final adjustments to gen_aig[e]fs_ics.py for production

[RussellManser-NCO]

This PR includes the last changes that SPA team made to

• oper/gen_aigfs_ics.py
• oper/gen_aigefs_ics.py

to operationalize the scripts. These changes are a band-aid fix that will need a coordinated fix in the next release. A PR such as #54 would likely resolve these issues. Some key areas we will need to improve on include:

• oper/gen_aigefs_ics.py
  • Remove boto initialization (caused failures during testing) and calls to download data from s3 buckets
  • Output netCDF file is still has mlgefs prefix, which is consistent with exaigefs_prep.sh
• Both scripts
  • Remove colon characters from intermediate file names
  • Explicitly locate files instead of looping and globbing (Look for input files explicitly instead of looping/globbing #36)

[aerorahul]

This isn't so bad.
v1.1 will hopefully make the S3 optional and will eliminate the need to comment it out.

[LinlinCui-NOAA]

This isn't so bad. v1.1 will hopefully make the S3 optional and will eliminate the need to comment it out.

@aerorahul Do we know when we need to have v1.1 ready?