[draft as this needs https://github.com/osbuild/images/pull/1655 and lacks a bunch of tests]

This branch provides a way to create an imageType from a bootc reference.

With that the API user can do:
```go
imgType, err := distro.ImageFromBootc(bootcRef, imgTypeName, archStr)
...
```
and that can then be passed to manifestgen.

/jira-epic HMS-8839