Add devfile urls to the Stack CRD

[kaczyns]

A Stack CR may point to a devfile rather than contain appsody-style artifacts. We will add two new fields to the spec section of the Stack CRD, which will link to devfile related artifacts:

apiVersion: kabanero.io/v1alpha2
kind: Stack
metadata:
  name: my-stack
  namespace: kabanero
spec:
  name: my-stack
  versions:
    - version: 0.0.1
      pipelines: (omitted for brevity)
      desiredState: active
      devfile:
      metafile:

Note the devfile and metafile. These point to the devfile.yaml and the meta.yaml respectively for a specific devfile. I am proposing that they can be one of https or gitRelease as support currently for the pipeline zips, and for the stack hub index in the Kabanero CR instance.

The stack controller will need to make sure it's in odo mode before acting on a Stack CR instance with devfile and metafile set (see #747 ). The specific actions to take are still being discussed, but for the time being:

1. The status.version[x].version should be set from metadata.version in the devfile
2. The status.version[x].images should be set by iterating the components[x] array in the devfile, and looking for elements that have a container set. The container will have an image and we can retrieve the digest for that image and put it in the Stack CR status. Note that there can be multiple images!
3. The status.version[x].pipelines should be set in the usual way.

There is an example devfile registry here, but note that this is subject to change:
https://github.com/elsony/devfile2-registry

Note that we are talking about v2 devfiles here.

[kaczyns]

This was implemented in #761