Ingest Fast Radio Burst candidates from CHIME

There has been renewed interest in ensuring that we ingest FRB candidates coming from CHIME during O4. This requires the following:

• Create/modify GCN listener to ingest events from CHIME
• Ensure FRB events can create external events either in their current form or with some wrapper function (i.e. get example GCN notice and see if can be uploaded directly)
• Contact GraceDB developers to add pipeline='CHIME' and search='FRB' if not already available
• Create new IGWN alert listener or modify GRB listener if similar enough to current workflow in order to fully include in RAVEN pipeline
• Determine expected rate (#/day) of FRBs from CHIME and whether individual significance (FAR?) of GRB is available or relevant (e.g. is very high significance so that FAR_FRB << FAR_GW?)
• Determine time windows used in coincidence search (CBC: [-2, +10]s, Burst: [-120, +600]s as in https://arxiv.org/abs/2203.12038?)
• Add relevant values to RAVEN pipeline (time window, raven.trigger_raven_alert) and add exceptions when different from GRB workflow
• Add testing via pytests, internal MDCs, and/or O3 replay to ensure system works as expected

These tasks could be split among individuals, especially between getting events ingested vs getting events processed later (likely my job).