Report Oban's configuration prefix and other improvements

Added

• Report Oban's configuration prefix value, if present, as a tag in Oban job samples. Thanks to @tfwright for suggesting and implementing this feature.

Changed

• Remove redundant cron check-in pairs. When more than one pair of start and finish cron check-in events is reported for the same identifier in the same period, only one of them will be reported to AppSignal.

View the Elixir package v2.15.5 changelog for more information.