Pkger field referencing within a package

As a user, I'd like the ability to reference fields within a package, so that I can create name changes that cascade throughout it.

Potentially something like the following with the fieldRef type. We can reference in absolute. Or reference it via the kind and grab the index/name of the field in question.

```yaml
apiVersion: 0.1.0
kind: Package
meta:
pkgName: pkg_name
pkgVersion: 1
description: pack description
spec:
resources:
- kind: Label
name: foo_label
- kind: Bucket
name: foo_bucket
associations:
- kind: Label
name:
fieldRef:
key: spec.resources[0].name
- kind: Dashboard
name: foo_dash
associations:
- kind: Label
name:
fieldRef:
key: labels[0].name
```