distro/rhel82: move ami output closer to official ec2 image

This includes adding (and excluding) the right packages, setting the right
systemd boot target, fixing kernel options, changing output type to
.raw.xz, and setting the size of the image to 6GB.

internal/pipeline/systemd_stage.go

@@ -3,6 +3,7 @@ package pipeline
 type SystemdStageOptions struct {
 	EnabledServices  []string `json:"enabled_services,omitempty"`
 	DisabledServices []string `json:"disabled_services,omitempty"`
+	DefaultTarget    string   `json:"default_target,omitempty"`
 }
 
 func (SystemdStageOptions) isStageOptions() {}