rhel84,osbuild2: add system ID to ISO

New stage option added in osbuild
https://github.com/osbuild/osbuild/pull/611

System ID is used by osinfo to identify the RHEL boot ISOs, where the
system ID is "LINUX".

internal/distro/rhel84/distro_v2.go

@@ -726,6 +726,7 @@ func (t *imageTypeS2) xorrisofsStageOptions() *osbuild.XorrisofsStageOptions {
 	return &osbuild.XorrisofsStageOptions{
 		Filename: t.Filename(),
 		VolID:    fmt.Sprintf("RHEL-8-4-0-BaseOS-%s", t.Arch().Name()),
+		SysID:    "LINUX",
 		Boot: osbuild.XorrisofsBoot{
 			Image:   "isolinux/isolinux.bin",
 			Catalog: "isolinux/boot.cat",

internal/osbuild2/xorrisofs_stage.go

@@ -7,6 +7,9 @@ type XorrisofsStageOptions struct {
 	// Volume ID to set
 	VolID string `json:"volid"`
 
+	// System ID to set
+	SysID string `json:"sysid,omitempty"`
+
 	Boot XorrisofsBoot `json:"boot,omitempty"`
 
 	EFI string `json:"efi,omitempty"`