Implement task log broadcasting via SocketIO. The logs aren't shown in the
web interface yet, but do arrive there in a Pinia store. That store is
capped at 1000 lines to keep memory requirements low-ish.
This also changes the order in which the task is updated; the activity is
now saved first, so that it can be included in the task status change
notification sent to SocketIO clients.
Manager now sends out task updates via SocketIO, and the web interface
handles those.
Note that there is a `BroadcastTaskUpdate()` function, but not a
`BroadcastNewTask`. The 'new job' broadcast is sent after the job's
tasks have been created, and thus there is no need for a separate
broadcast per task.
SocketIO clients can now send a message with `/subscription` event type
in order to subscribe to or unsubscribe from job-related updates.
These job-related updates themselves aren't sent yet, so this is a change
that's impossible to really test. The socketIO code for joining/leaving
rooms is called, though.
By having all info for the jobs table in the `JobUpdate` schema, it won't
have to query for the full job when a new job is added. This fetching of
the full job is now delayed until someone clicks on the table row.
