Make the ostree commit spec mandatory in the OSTreeInstaller ImageKind.
The installer image type is not just for ostree types so make the ostree
parameters optional for the ISOTree Pipeline.
Use the ostree.CommitSpec to specify commits parameters.
Don't pass blueprint Users and Groups options all the way down to the
osbuild stage bindings. Instead, convert them to the internal
users.User and users.Group structs.
Ideally we would do this even higher up in the code path, before
reaching the distro, but this is the first step towards that.
- Use newer granular stages to build the bootiso tree rather than the
deprecated bootiso.mono stage.
- Adjust the ISOTree struct properties: add the ones needed by the new
stages and remove any properties that have been moved to the new
pipelines.
Implement all of Fedora in terms of this new abstraction. What used to be the
manifest functions (and before that the pipeline functions) are now the image
functions, whose purpose is to instantiate the right image kind structs from the
image type definitions we currently have in the distro definition.
