Use it to define location of experimental_obs.

Refs NOAA-EMC#2683

…al_obs_path

* origin/develop:
  Update global atmos upp job to use COMIN/COMOUT (NOAA-EMC#2867)
  Update config.resources for bufr sounding job postsnd (NOAA-EMC#2917)
  Cleanup job for GEFS (NOAA-EMC#2919)
  Build GDASApp and unset memory in Gaea-C5 xml files (NOAA-EMC#2912)
  add 1 deg ocean/ice info to parm/config/gfs/config.resources (NOAA-EMC#2922)
  Support gefs C48 on Azure (NOAA-EMC#2881)
  Disable native grid writes for non-JEDI experiments; update C384 compression options (NOAA-EMC#2914)

…nto feature/marinevar

* origin/feature/experimental_obs_path:
  Introduce BASE_DATA variable