ssa: add DriftIgnoreRules to ApplyOptions for field-level ignore on apply

[dipti-pai]

Changes include

• Add []jsondiff.IgnoreRule to ssa ApplyOptions
• Change has no effect in create code paths. In Apply and ApplyAll code paths that correspond to update, remove ignored fields matching the ignored rules from the object.

Includes tests for various scenarios for optional and mandatory fields, claiming shared/forceful ownership and orphaning owned fields without a manager.

1. When drift ignore rules are specified for optional fields:

• flux manager drops ownership of the ignored fields.
• If another manager co-owned or claimed force ownership, the field values are set accordingly.
• If no field manager is present, the field is dropped and garbage collected by Kubernetes.

2. When drift ignore rules are specified for mandatory fields:

• If another manager co-owned or claimed ownership of the fields forcefully, Flux drops ownership of the field. Once Flux drops ownership, the other manager cannot drop ownership of the mandatory field, they get an error.
• If no other manager claims ownership of the fields, flux cannot drop ownership of the field and returns an error.

Associated kustomize controller draft PR testing the changes from controller perspective - fluxcd/kustomize-controller#1627

Fixes: #696

[matheuscscp]

The code is looking great to me, but I'd like to better understand how applying the ignore rules after dry-run works. I'm not saying it's not correct at all, just saying that it's probably correct and I need to catch up and understand the whole flow. It would be great if we could talk about this in the next dev meeting 🙏