manifest: introduce GetPackageSetChains()

This returns the package set chains for a given manifest. A package
chain is a list of depsolve requests (include, exclude, repos) to be
performed in sequence as if packages were incrementally installed
to the same image. Each pipeline has its own package set chain, and
the manifest returns a mapping from pipeline name to their
respective chain.

So far this is not used, and always returns the empty chains.

The intention is to eventually make each pipeline (and hence
manifest) self-describing, so they can return exactly the depsolve
requests needed to serialise them, rather than relying on that
information being maintained externally.

internal/manifest/manifest.go

@@ -58,6 +58,16 @@ func (m *Manifest) addInline(data []string) {
 	m.inlineData = append(m.inlineData, data...)
 }
 
+func (m Manifest) GetPackageSetChains() map[string][]rpmmd.PackageSet {
+	chains := make(map[string][]rpmmd.PackageSet)
+
+	for _, pipeline := range m.pipelines {
+		chains[pipeline.Name()] = pipeline.getPackageSetChain()
+	}
+
+	return chains
+}
+
 func (m Manifest) Serialize() (distro.Manifest, error) {
 	var commits []ostree.CommitSource
 	for _, commit := range m.osTreeCommits {

internal/manifest/pipeline.go

@@ -13,6 +13,7 @@ import (
 
 type Pipeline interface {
 	Name() string
+	getPackageSetChain() []rpmmd.PackageSet
 	serialize() osbuild2.Pipeline
 	getPackageSpecs() []rpmmd.PackageSpec
 	getOSTreeCommits() []osTreeCommit
@@ -34,6 +35,10 @@ func (p BasePipeline) Name() string {
 	return p.name
 }
 
+func (p BasePipeline) getPackageSetChain() []rpmmd.PackageSet {
+	return []rpmmd.PackageSet{}
+}
+
 func (p BasePipeline) getPackageSpecs() []rpmmd.PackageSpec {
 	return []rpmmd.PackageSpec{}
 }