Use `INC` directive in the various machine config files to point to a single observations config file

[guillaumevernieres]

Thanks for adding the marine bufr dump configs to the other machine. Would it make sense to have an INC directive in the various machine config files pointing to a single file with the observation configs, to reduce unneeded superfluous redundancy?

Originally posted by @AndrewEichmann-NOAA in #83 (review)