/status endpoint should not transition from "Starting" to "Running" before the application is fully ready

Currently, the /status endpoint uses pluginFrameworkStartedEvent to determine when to transition from STARTING to RUNNING.

However we should wait until all upgrade tasks and plugin upgrade tasks are done - it would be better to listen to one of the application started type events.

Right now Confluence nodes look like they are ready to serve before they are, causing issues with load balancers etc.