[feat] support skipping manifests in SyncSSA

[Unix4ever]

If the manifest is skipped, neither update nor delete should happen.
Ideally it would be nice to specify the list of manifest IDs to skip through the opts parameter.

What's the purpose of that: in Omni some manifests should support create only mode. Such manifests will be used in bootstrap mode, like deploying ArgoCD then ArgoCD will manage itself.

See: siderolabs/omni#2172

[Orzelius]

I think creating a new helper, something like manifests.CreateOnly with a similar call signature to manifests.SyncSSA would make sense here. The helper would only create objects and never prune or modify.

Benefits of this approach:

• If pruning or modification of objects becomes desirable manifests.SyncSSA can be easily used in it's place
• a different inventory and inventory policy can be specified for the given objects

On omni side I think it would still make sense to keep track of if an object has already been created to avoid unnecessary calls to kubernetes.

Would this work instead?

[Unix4ever]

Yeah, I think so.
I'm thinking to extract the one time manifests to a separate inventory.

Actually it's probably easy to solve without changing go-kubernetes library if I do it.
Can run manifests.SyncSSA with NoPrune, while dropping the manifests that already exist from the list. This way update won't be applied, but the manifests won't be removed due to NoPrune