Generalize environmental data pulling/appending functionality.

[jackVanish]

Is your feature request related to a problem? Please describe.
Building on the success we had in importing/merging geo-linked bathymetry data, we want to start generalizing remora's data ingestion functionality to allow arbitrary variables pulled from arbitrary sources.

Describe the solution you'd like
Understanding that there are restrictions on the type of data that can be pulled (right now, needs to be a geotif format), we want to be able to provide an arbitrary source and an arbitrary variable. That means gutting the hard-coding in Remora's functions to do with data pulling and rebuilding it to allow for a more flexible approach. Bathymetry has provided a proof of concept for how this can begin, seen here: https://github.com/ocean-tracking-network/remora/blob/thredds_expansion/R/pull_var_arbitrary.R.

[jdpye]

Saw a repository over at Axiom Data Science for this Ocean Data Gateway API - they have ERDDAP and THREDDS hooks among others that give a time/space search for in-situ ocean data collected. I'm not sure if this is useful but it bears investigating a bit further to try and serve this functionality.

https://ocean-data-gateway.readthedocs.io/en/latest/api.html