RHEL-90: use XBOOTLDR partition GUID for /boot

Use the Extended Bootloader Partition GUID for `/boot`, instead of the
Linux filesystem data GUID. This is useful for autodetection of a
partition purpose based on its GUID without reading the `/etc/fstab`
first.

Ensure that when creating mountpoints, e.g. when converting the
partitions layout to LVM, the `/boot` partition get the proper GUID
assigned.

Regenerate RHEL-90 and centos-9 image test cases.

Related to https://bugzilla.redhat.com/show_bug.cgi?id=2057231

internal/disk/disk.go

@@ -45,6 +45,9 @@ const (
 	PRePartitionGUID = "9E1A2D38-C612-4316-AA26-8B49521E5A8B"
 
 	RootPartitionUUID = "6264D520-3FB9-423F-8AB8-7A0A8E3D3562"
+
+	// Extended Boot Loader Partition
+	XBootLDRPartitionGUID = "BC13C2FF-59E6-4262-A352-B275FD6F7172"
 )
 
 // Entity is the base interface for all disk-related entities.

internal/disk/partition_table.go

@@ -179,7 +179,12 @@ func (pt *PartitionTable) CreateMountpoint(mountpoint string, size uint64) (Enti
 	var maxNo int
 
 	if pt.Type == "gpt" {
-		partition.Type = FilesystemDataGUID
+		switch mountpoint {
+		case "/boot":
+			partition.Type = XBootLDRPartitionGUID
+		default:
+			partition.Type = FilesystemDataGUID
+		}
 		maxNo = 128
 	} else {
 		maxNo = 4