Add pihole-FTL.conf to teleporter

/etc/pihole/pihole-FTL.conf can be customized to set values used at FTL startup.
It makes sense to export it to be saved.

I think all those files should be exported/teleported for settings backup or moving to another device:
/etc/pihole/whitelist.txt
/etc/pihole/black.list
/etc/pihole/blacklist.txt
/etc/pihole/regex.list
/etc/pihole/adlists.list
/etc/pihole/dhcp.leases
/etc/pihole/pihole-FTL.conf
/etc/pihole/setupVars.conf

This feature request will be implemented by

Implemented with v5.1
https://pi-hole.net/2020/07/15/pi-hole-5-1-released/