Follow-up from "set pipeline preferred events"

The following discussion from !997 (merged) should be addressed:

• @cody.messick started a discussion: (+6 comments)

  I think we need to add buttons to the dashboard that change pipeline preferred events. There were times in O3 when the preferred event was changed manually before sending initial alerts, the same is likely to happen for preferred pipeline events. We'll also need changes to the unit tests for the new buttons.

Add buttons on flask dash board to manually select pipeline preferred events