Validate Test Specification Schema

[twobiers]

During my experiments with xprin, I've noticed that xprin happily accepts an invalid test specification, e.g. (See tests[0].observed-resources):

common:
  inputs:
    functions: ../_shared/functions.yaml
    composition: ./composition.yaml
    xr: ./xr.yaml
    extra-resources: ./extra-resources
    crds:
      - ../../../apis
      - ../../../crossplane.yaml

tests:
  - name: "First reconcilation loop creates User Assigned Identity"
     observed-resources: # Note that we have not placed observed resources under `inputs`
       - ./observed
     assertions:
      - name: "user-assigned-identity-exists"
        type: "Exists"
        resource: "UserAssignedIdentity/example-identity"

I think it would be good if xprin would error out here.

Additionally, it would be cool to generate a JSON Schema from the type definition, so one could point the IDE to it for autocompletion/IntelliSense.