we want to move to a state where composer is a stateless service,
therefore we cannot take blueprints by name (and fetch them from a
storage) or assume repositories by the distribution. This commit
introduces both of these parameters as part of the structure.
In the current state, osbuild-pipeline exits with random golang error,
such as goroutine failed, which is not at all helpful. This PR
introduces CLI arguments validation and helful error messages that use
the newly introduced types so that we don't waste time guessing what
was the right way to invoke this tool.
We currently use strings for passing arches and image types around,
which is not ideal. We should have a finite set of supported image types
and architectures as well as upload targets. This PR introduces custom
types to make the code base more readable and possibly also more
correct.
I considered some alternatives like a struct with private fields, but struct cannot
be const, so that does not help either. Eventually I think this is the "get s**t done"
solution.
The package also includes unit-tests which try to convert string to
structure and the other way around to make sure it all works properly.
