The `FilesInputs` was since the beginning an XZ-specific implementation
of the input, but it was implemented in the `files_input.go` in a false
hope that it could be used as a generic stage inputs by any stages. It
turned out that various stages require different implementation of
its input. Specifically there is usually a stage-specific key, which has
assigned a common input type. For XZ stage, the key is `file`.
Remove `FilesInputs` and instead implement `XzStageInputs` which is now
accepted by the XZ stage.
Fix all affected pipeline implementations that use XZ stage.
Signed-off-by: Tomáš Hozza <thozza@redhat.com>
Rework files input implementation to support all reference types
supported by the input schema. Also implement helper functions to
generate supported reference types. In some cases, the reference
supports e.g. referencing multiple pipelines in the stage inputs, but
this is currently not implemented, since no pipeline in composer uses
it.
Rework the files input unit tests to cover the new functionality.
Adjust all code affected by the changes made to files input.
Signed-off-by: Tomáš Hozza <thozza@redhat.com>
