Add additional events for cron jobs

[matt2e]

Events like:
"could not build body for cron job"
"Could not kill stale cron job %q because schedule could not be parsed: %q"

all of these log messages should be associated with the cron job in the events table so that the user can filter and find issues with their cron jobs.

[matt2e]

This may end up being rolled into async calls work

[safeer]

Cron is rewritten to use async_calls, so this is a dupe of #2473