Add installer VNC configs with different labels for images with grub bootloader

features.in/syslinux/cfg.in/25grub-install-vnc-connect.cfg

+label vncconnect
+  menu label VNC client (edit to set server IP address)
+  kernel alt0/vmlinuz
+  append initrd=alt0/full.cz changedisk fastboot automatic=method:cdrom ramdisk_size=@altinst_size@ showopts @bootargs@ headless vncconnect=IP
+

features.in/syslinux/cfg.in/25grub-install-vnc-listen.cfg

+label vncpasswd
+  menu label Install @relname@ (headless with DHCP+VNC) (password VNCPWD)
+  kernel alt0/vmlinuz
+  append initrd=alt0/full.cz changedisk fastboot automatic=method:cdrom ramdisk_size=@altinst_size@ showopts @bootargs@ headless vncpassword=VNCPWD
+

features.in/syslinux/config.mk

@@ -41,6 +41,8 @@ use/syslinux/%.cfg: use/syslinux
 
 ifeq (,$(filter-out ppc64le,$(ARCH)))
 use/syslinux/localboot.cfg use/syslinux/removable.cfg use/syslinux/lateboot.cfg use/syslinux/sdab.cfg: use/syslinux; @:
+use/syslinux/install-vnc-connect.cfg: use/syslinux/grub-install-vnc-connect.cfg; @:
+use/syslinux/install-vnc-listen.cfg: use/syslinux/grub-install-vnc-listen.cfg; @:
 endif
 
 use/syslinux/timeout/%: use/syslinux