Make the FTL log tail optional. Pass in TAIL_FTL_LOG: 0 to silence it

[PromoFaux]

What does this PR aim to accomplish?:

See title. By default the image will tail the FTL log. Users can disable this if it is too noisy for their preference

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[edgd1er]

If no logs are required may be pihole-FTL could be started et kept in foreground ('-f)

[PromoFaux]

If we did that, then the container would stop if ever FTL was restarted/stopped.

For now at least I'd like to keep the command as-is

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

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[PromoFaux]

If no logs are required may be pihole-FTL could be started et kept in foreground ('-f)

Something else I realised in doing some testing this evening. I am not sure what it is, but I remember it happening on v5 container too, if we start pihole-FTL in the foreground, it stops outputting to the docker log. Note there are more lines in the actual file than there are on the bottom half of the screen:

[DL6ER]

What is actually puzzling here is that it stops right in the middle of reporting the database statistics. They are simply a collection of printf statements, there is nothing in the code that could actually make it stop after the first line:

https://github.com/pi-hole/FTL/blob/5753b50df40defa15d16f6989e12a9ecf3439be9/src/log.c#L502-L512

[github-actions]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[github-actions]

Conflicts have been resolved.

[PromoFaux]

Marked conversation about init systems as outdated due to #1406 being merged.

Starting FTL in the foreground leads to weirdness with the output where it just cuts out - see previous two comments. This works well enough. Either we tail the log or we don't. Simples.

[yubiuser]

Needs documentation of the new env setting.

[PromoFaux]

@yubiuser #1429