Display task TTL

https://redmine.teklia.com/issues/8785

Requires backend#1871 and #1513 (closed)

The task execution time label in the process status view should now also display the TTL using the same duration display helper.

A task that has a TTL of 600 (10 minutes) and that has been running for 3 minutes would be shown as 03:00 / 10:00.

A task that has a TTL of 0 (infinite) and that has been running for an hour can use an infinity symbol: 01:00:00 / ∞.

A task that currently has no execution time (where started is not set) should show an em-dash instead: — / 10:00, — / ∞.

Both durations have two different title attributes. The execution time keeps the same title as before, and the TTL has Maximum execution time: {secondsToTimedelta() or "Infinite"}.