scheduler: restarting completed workflows

[oliver-sanders]

Umbrella issue to cover issues related to extending completed workflows:

• Make it easier to restart a completed workflow.
• Make it more obvious why a completed workflow shuts down.
• Make it easier to extend a completed workflow run (i.e. by triggering extra stuffs).

Work:

• Timeout on restarting completed workflows #5231
• Tweak triggering when no flows present #5084
• easier way to select cycle start tasks #5416
• Document (extend the interventions section interventions cylc-doc#626)

[hjoliver]

Make it easier to restart a completed workflow.

Is the existing timeout PR not sufficient in your opinion? #5231

Make it more obvious why a completed workflow shuts down.

Agreed, at the least we can log an explanatory message.

Make it easier to extend a completed workflow run (i.e. by triggering extra stuffs).

How is this bullet point different from the first one?

[oliver-sanders]

Is the existing timeout PR not sufficient in your opinion? #5231

Yes, I've put this up as an umbrella issue to make it easier to track the larger functionality as no single PR addresses the whole issue.

How is this bullet point different from the first one?

Extending a workflow run e.g. by adding a new cycle of tasks is not completely solved by #5231 because it requires the user to know exactly which tasks they need to trigger to kick off the new cycle. This bullet point covers the point that this should be simple & transparent for non-techinical users and, ideally require a minimal number of operations to achieve.

The suggestions in #5416 would make this much more user-friendly.