Add new external pipeline EinsteinProbe

Similarly to #255 (closed), we want to add a new external pipeline EinsteinProbe.

Since the work to convert the native JSON notices to a standard VOEvent XML file has already been completed and we expect to use the existing GRB search field, we don't anticipate any work is needed to change ingestion. See: emfollow/gwcelery!1516 (merged)

GWcelery issue: emfollow/gwcelery#846

GWCelery MR: emfollow/gwcelery!1503 (closed)

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