manifest: return inline FDO cert from CoreOSInstaller pipeline

The CoreOSInstaller pipeline supports adding inline data to the tree for
the FDO cert.  This needs to be returned by the pipeline object via the
getInline() method to attach the necessary data to the Sources array in
the manifest.

internal/manifest/coreos_installer.go

@@ -126,6 +126,14 @@ func (p *CoreOSInstaller) serializeStart(packages []rpmmd.PackageSpec) {
 	}
 }
 
+func (p *CoreOSInstaller) getInline() []string {
+	// inline data for FDO cert
+	if p.FDO != nil && p.FDO.DiunPubKeyRootCerts != "" {
+		return []string{p.FDO.DiunPubKeyRootCerts}
+	}
+	return []string{}
+}
+
 func (p *CoreOSInstaller) serializeEnd() {
 	if len(p.packageSpecs) == 0 {
 		panic("serializeEnd() call when serialization not in progress")