Disable flush_logs endpoint inside docker containers

[rdwebdesign]

What does this PR aim to accomplish?

The flush process needs a FTL restart, but this is not possible inside docker containers (not enough permissions). Currently, if the API endpoint is called inside a container, it returns "success" and FTL logs success messages, but in reality FTL is never restarted and the process is not correctly completed.

This PR effectively disables the flush_logs endpoint when FTL is inside a container. Inside containers the API will respond with 403 forbidden.

This is related to: pi-hole/pi-hole#6391

How does this PR accomplish the above?

FTL checks if it is running inside docker and, if so, returns a 403 error message.

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[yubiuser]

Does it really need a restart when triggered via the API? At least on bare metal it does not perfome a restart

2025-10-22 09:02:58.204 CEST [266807/T267169] INFO: Received API request to flush the logs
2025-10-22 09:02:58.473 CEST [266807/T267169] INFO: Log has been flushed due to API request

But as I said in the other PR: we might want to disable FTL restart option via API when running on docker.

[DL6ER]

FTL can restart just fine in docker as the binary is able to restart within itself without the need for an external helper like systemd. It doesn't exit, either, so the docker container should also not think it's dead. When we disable the ability to restart we also remove the ability to all the settings that do need a restart because dnsmasq configuration is changed.

[DL6ER]

Currently, if the API endpoint is called inside a container, it returns "success" and FTL logs success messages, but in reality FTL is never restarted and the process is not correctly completed.

What do the logs show?

[DL6ER]

@rdwebdesign I am setting this back to draft. It seems there are a few things we need to clarify before this can be merged (including if this change is needed at all)

[rdwebdesign]

(including if this change is needed at all)

Yes. I'm not sure if this is needed at all.

Apparently we need to change how Web handles some things and not try to use pihole flush command from web interface.