Allow other FTL process inside docker

[DL6ER]

What does this implement/fix?

Do not refuse to (re)start if there is another pihole-FTL process already running inside a docker container on the same host.

Currently, (re)starting on the host is prevented when FTL detects during startup that another process is running on the machine (the one inside the container) even when they can obviously run alongside perfectly fine. This is caused by the host being able to see all processes, not only the one in its own container, i.e., in its own cgroup*. This actually hinders development/testing natively on the host.

This commit fixes this by not considering pihole-FTL processes running in downstream (!) docker containers as duplicate instances.

How can this be reproduced? After installing Pi-hole natively on a device, also start a docker container running pihole-FTL. Then, try to restart pihole-FTL on the host and observe that this is prevented as the task running inside the container is considered a duplicate process. This is quite obviously a false-positive detection.

*) Docker utilizes cgroups to control and limit the resources available to containers.

This is a regression of #2025

---

Related issue or feature (if applicable): N/A

Pull request in docs with documentation (if applicable): N/A

---

By submitting this pull request, I confirm the following:

1. I have read and understood the contributors guide, as well as this entire template. I understand which branch to base my commits and Pull Requests against.
2. I have commented my proposed changes within the code.
3. I am willing to help maintain this change if there are issues with it later.
4. It is compatible with the EUPL 1.2 license
5. I have squashed any insignificant commits. (git rebase)

Checklist:

• The code change is tested and works locally.
• I based my code and PRs against the repositories developmental branch.
• I signed off all commits. Pi-hole enforces the DCO for all contributions
• I signed all my commits. Pi-hole requires signatures to verify authorship
• I have read the above and my PR is ready for review.

[yubiuser]

Tested. Works nicely as described.