optimise Download history page refresh

[acumarav]

Download history page is refreshing every 5 secs https://athena.ohdsi.org/vocabulary/download-history The main reason for this - is to refresh the status of PENDING bundle. It will be more optimal to refresh only if there is at least one PENDING bundle or use websocket push to trigger a refresh when the bundle is assembled

[mik-ohdsi]

(a manual refresh would also still be acceptable...)