Ensure proper file ownerships if pihole-FTL is started as root

[DL6ER]

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When started as root, e.g., because capabilities are not available on the current system, we drop from root to some unprivileged user as soon as we did everything we needed to do as root (open privileged ports, etc.).

Unfortunately, the log and database files were still owned by root in this case and hence no further logging was possible, neither to the database nor to the pihole-FTL.log file.

This PR fixes a bug discussed on Discourse.

This template was created based on the work of udemy-dl.

[pralor-bot]

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

https://discourse.pi-hole.net/t/ftldns-upgrade-failed-solved/12022/48

[AzureMarker]

This PR requires pi-hole/pi-hole#2394