Expose metrics from NGINX and Bind to Prometheus

[The0mikkel]

This update is the docker-compose update for the NGINX and Bind export to Prometheus.

Please see #38 for further information about this update as this solves #38

In short, we have added two exporters, to export status from Bind and NGINX, such that Prometheus can scrape the data.
This update also includes network segregation, such that the exporters only have access to the services they need, and no more.
And we have updated the README.md, to include a short description of how to use the metrics.

[stale]

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[The0mikkel]

This is still awating review.
Since original creation, it has been tested and used at multiple LAN parties.

When looking at the issue, there seems to be an interest in getting these features. If not all, then some.

[stale]

This issue has been automatically marked as inactive because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[The0mikkel]

This is still awating review.

[Lepidopterist]

I think this is a nice addition, but I'm torn as to whether it should be included by default.

My gut feeling would be to include the env var in the .env file, but provide a "docker-compose.yml.prometheus" that can be used if you want to run with the Prometheus backend. We can update the Readme.md to include instructions to run with the Prometheus backend. Thoughts @lancachenet/core ?

[The0mikkel]

Having an alternative docker compose file, would definitely allow for flexibility, while preserving ease of use for current users.
It could easily be used with docker compose -f prometheus.docker-compose.yml up -d, utalizing the -f flag.

The update does not really need the .env update (or it is so small, it won't impact the "simple" version). Making a seperate for that would probably be overkill.

Looking at the docker-compose.yml file now, I can see that multiple elements have changed in the Docker compose ecosystem since it was written.
A strong example of this, is the removal of version being required (and now throwing a warning in up-to-date systems. I'm no fan of this...).
But let that be an element for another update.

[The0mikkel]

I have updated the PR with the metrics exports being split into a seperate file called docker-compose.metrics.yml, and added a lot more documentation on the use of the exports, as well as added grafana dashboards for them.

Just to note, the lancachenet/lancache-dns#140 PR needs to be merged, before the metrics docker compose file will work correctly.

[Lepidopterist]

Also LGTM, based on the lancache-dns changes being merged.

[Lepidopterist]

FYI, we have an event next week so we will likely test it off there before fully committing the PR.

[The0mikkel]

If anything seems unclear, when setting up the system, then you are more than welcome to reach out, so that we can get that fixed and documented.
Quite a good thing to test it, before committing.