Build iso and host from Rancher

[agracey]

When a MachineRegistration is created, we should give an option to build the iso and host it from the upstream cluster.

A POC of what this could look like is at: https://gist.github.com/agracey/9d053ca7e0adef6fe7e8bb9b7687f4f9

And I'm working on an improved version of this at: https://gist.github.com/agracey/b0eedb7eef7094558197f94a7689f238

(As with all of my POCs, feel free to ignore 🤣 I built it because I needed easier demo builds on limited hardware)

There are a few changes that I think would be needed to make this a reality:

• Addition of Elemental Teal version (OCI tag) to MachineRegistration spec
• An nginx or other hosting option and the persistent volume underneath (Maybe the s3gw project if it's ready enough?)

[davidcassany]

rancher/elemental-cli#336 could help on making this procedure lighter, since it allows to add a yaml into an existing iso on the fly.

[kkaempf]

Now tracked at rancher/elemental-operator#207