Create sky map for offline targeted sub-threshold GRBs from Swift and Fermi
Currently the function to create external sky maps is triggered off GCN notices here: https://git.ligo.org/emfollow/gwcelery/-/blob/master/gwcelery/tasks/external_triggers.py#L169
We also want to create sky maps for targeted sub-threshold GRBs as well, which are uploaded 'by hand' so we need another path for this to occur.