If this is still needed at some point, it can be added to the
flamenco-manager.yaml file instead; it then doesn't require any source
code changes or redeploys, just a restart of Flamenco Manager.

The Manager will return a 409 Conflict status for updates to tasks that
have been assigned to another worker. This change prevents the worker
from trying to push these updates indefinitely to the Manager.

The task timeout checker runs periodically, but only starts 5 minutes after
manager startup. This allows workers to push updates to the manager after
downtime, before getting timed out. This /timeout URL is there to allow
enforcing timeouts within that 5 minute window.

MergeExrCommand is now called MergeProgressiveRendersCommand, to be
consistent with the job compiler on Server.

Now tasks can be sorted by job and task priority, and different tasks can
have different priorities within a job. This will allow for better control
over task ordering than just relying on parent relationships.

Tasks are sorted by job priority first, and then by task priority.

This is quite useful if one task failed (for example when a worker times
out) and you want to re-queue it without cancelling any currently active
tasks.

When 'src' needs to be moved to 'dst', but 'dst' already exists, the
command finds a suffix that doesn't exist yet.

This improves performance when dealing with large graphs.