Resume/suspend/terminate/stop will result in invalid state

[alexec]

Summary

Only the workflow controller should be able to change a workflow.

Motivation

All these operations can result in invalid state one large workflows because they update the workflow out of the main loop.

Proposal

The controller currently reacts to pod and workflow changes, but it can already be reacting when a third-party changes - resulting in conflict and invalid state.

We could have a new operation queue that takes operations to workflows and ensures they are applied sequentially.

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[alexec]

See #2367

[agilgur5]

I think this is no longer an issue? We have several checks in the codebase where the ShutdownStrategy is handled currently.

If they require changes to the Workflow (via spec or annotation or label), then they are more-or-less queued up as resourceVersion changes.

Only the workflow controller should be able to change a workflow.

Related is #12538 for the manual Retry operation

We could have a new operation queue that takes operations to workflows and ensures they are applied sequentially.

Also *Request CRDs as I mentioned in #6490 (comment) would very explicitly delegate to the Controller and would be queued (as the entire Controller is queued).