lxd: Include CAP_SYS_ADMIN in rsync AppArmor profile (#14231)

The `CAP_SYS_ADMIN` cap is required for rsync to write to files using
security.* xattrs. In order to preserve these xattrs and ensure proper
updates when these xattrs are present, we must include this capability
in the rsync AppArmor profile.

Related: #13707.

lxd/apparmor/rsync.go

@@ -29,6 +29,7 @@ profile "{{ .name }}" flags=(attach_disconnected,mediate_deleted) {
   capability fsetid,
   capability mknod,
   capability setfcap,
+  capability sys_admin,
 
   unix (connect, send, receive) type=stream,