WIP: Upload external sky map automatically; create one if no fits file available

Currently external sky maps are only uploaded when a combined sky map is created (which does not work correctly because of the fact the GW sky maps are in G-events not superevents.)

This merge request makes it so that whenever we get a GCN notice we try to download an external sky map. If none is available (i.e. we haven't downloaded one yet) an approximate Gaussian sky map will be created using the RA, dec, and error radius given in the GCN notice (we will keep creating approximate sky maps every GCN notice since the localization can improve until we download an official one.)

• Grab/upload or create an external map from GCN values if none is available
• Verify created sky map is correct (coordinate system, etc.)
• Unittest orchestrator functions
• Unittest external trigger pipeline
• Unittest sky map creator