Rancher UI Extensions

[sudomateo]

#1 described creating an initial Oxide Rancher UI extension but it ended up being more of a scaffolding than an entire extension. This issue tracks the work of actually creating a Rancher UI extension.

At a minimum we'll need the following.

• A Cloud Credential component.
• A Machine Config component.
• CI/CD to build and release the UI extension.
• Documentation for users to install and use the UI extension.

[linear]

SSE-163