Ingest GCN VOEvents from SVOM

Requested by @rachel.hamburg, we want to start ingesting VOEvents from SVOM as another GRB search.

Here's an example of a notice:

sb23041100_eclairs-wakeup_2.xml

This will require the following changes

• Add pipeline='SVOM' as mentioned in #255 (closed)
• Add SVOM external events to IGWN alert
• Modify translator to ingest the particular notice values, such as adding "Burst_Id" to get the ID and "Exposure" to get the duration.