Add systemctl status --full --no-pager pihole-FTL.service to the debug log

[yubiuser]

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• I have made only one major change in my proposed changes.
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What does this PR aim to accomplish?:
Adds the output of systemctl status --full --no-pager pihole-FTL.service to the debug log. This is a usual follow up question during support in case FTL is not running.

*** [ DIAGNOSING ]: Pi-hole processes
[✓] lighttpd daemon is active
[✓] pihole-FTL daemon is active

*** [ DIAGNOSING ]: Pi-hole-FTL full status
   ● pihole-FTL.service - LSB: pihole-FTL daemon
   Loaded: loaded (/etc/init.d/pihole-FTL; generated)
   Active: active (exited) since Thu 2020-11-19 12:30:07 CET; 4 days ago
     Docs: man:systemd-sysv-generator(8)
  Process: 23694 ExecStart=/etc/init.d/pihole-FTL start (code=exited, status=0/SUCCESS)

Warning: Journal has been rotated since unit was started. Log output is incomplete or unavailable.

*** [ DIAGNOSING ]: Setup variables
    CONDITIONAL_FORWARDING=false
    TEMPERATUREUNIT=C
    DHCP_START=192.168.1.20

[pralor-bot]

This pull request has been mentioned on Pi-hole Userspace. There might be relevant details there:

https://discourse.pi-hole.net/t/pi-hole-core-web-v5-2-and-ftl-v5-3-released/40909/1