feat(vmop): add operation supersede flow

[danilrwx]

Description

Add the first VMOP supersede flow for compatible VirtualMachineOperation pairs.

Implemented changes:

• add Superseded reason for the Completed VMOP condition;
• add a supersede matrix for allowed and forbidden operation pairs;
• allow admission for compatible supersede combinations and reject forbidden active-operation combinations;
• mark older active VMOPs as Completed with Completed=True and reason=Superseded;
• clean up older operation side effects for Start, Restart, Migrate and Evict;
• make Stop idempotent when VMI is already absent;
• make force Restart start a VM when VMI is absent;
• add unit coverage for supersede scenarios;
• document VMOP supersede behavior in the user guide.

Why do we need it, and what problem does it solve?

Previously, any active VMOP for a VM blocked newer VMOPs until it finished. This made recovery and escalation scenarios inconvenient: for example, a pending Start could not be interrupted by Stop, and a graceful Stop could not be escalated to force Stop.

The supersede flow lets a newer compatible operation take precedence, safely completes the older operation as superseded, and lets the newer operation continue normally.

What is the expected result?

1. Create a VMOP that stays active for a VM.
2. Create a compatible newer VMOP for the same VM, for example:
   • Start -> Stop;
   • Stop -> Stop(force).
3. Verify the older VMOP has:
   • status.phase: Completed;
   • Completed=True;
   • reason=Superseded.
4. Verify the newer VMOP continues and completes normally.
5. Create a forbidden pair, for example Stop -> Start or Start -> Start, and verify admission rejects the newer VMOP while the older operation is active.

Checklist

• The code is covered by unit tests.
• e2e tests passed.
• Documentation updated according to the changes.
• Changes were tested in the Kubernetes cluster manually.

Changelog entries

section: core
type: feature
summary: Allow compatible VirtualMachineOperations to supersede older active operations.