osbuild: add support for org.osbuild.container inputs

Add bindings for `org.osbuild.conainer` inputs which can be used to
supply containers to stages. Currently only fetching containers via
sources is supported.

internal/osbuild/containers_input.go

@@ -0,0 +1,46 @@
+package osbuild
+
+import (
+	"github.com/osbuild/osbuild-composer/internal/container"
+)
+
+type ContainersInputReferences interface {
+	isContainersInputReferences()
+}
+
+type ContainersInputSourceRef struct {
+	Name string `json:"name,omitempty"`
+}
+
+type ContainersInputSourceMap map[string]ContainersInputSourceRef
+
+func (ContainersInputSourceMap) isContainersInputReferences() {}
+
+type ContainersInput struct {
+	inputCommon
+	References ContainersInputReferences `json:"references"`
+}
+
+const InputTypeContainers string = "org.osbuild.containers"
+
+func NewContainersInputForSources(containers []container.Spec) ContainersInput {
+	refs := make(ContainersInputSourceMap, len(containers))
+	for _, c := range containers {
+		ref := ContainersInputSourceRef{
+			Name: c.LocalName,
+		}
+		refs[c.ImageID] = ref
+	}
+
+	return ContainersInput{
+		References: refs,
+		inputCommon: inputCommon{
+			Type:   InputTypeContainers,
+			Origin: InputOriginSource,
+		},
+	}
+}
+
+type ContainersInputs map[string]ContainersInput
+
+func (c ContainersInputs) isStageInputs() {}