feat(metrics_server): Add Bandit support

[odarriba]

Change description

Updaters the metrics server child spec to support Bandit if available, as it is the new standard in Phoenix.

What problem does this solve?

It solves the need of exposing metrics in an internal port while using Bandit as the Plug server in newer/updated Phoenix apps.

Related issues: #265

Example usage

1. Create a new Phoenix app with Bandit
2. Add PromEx and configure the metrics server:

config :your_app, YourApp.PromEx,
  metrics_server: [
    port: 9200,
    path: "/metrics",
    protocol: :http,
    auth_strategy: :none
  ]

Additional details and screenshots

Screenshot of the standalone metrics server starting with Bandit:

Checklist

• My changes have passed unit tests and have been tested E2E in an real project.

[odarriba]

@akoutmos I'm not surte if this lib is still maintained, just in case pinging you to see if we can get a review at some point 🙏 Thanks for your time and work for this lib 🙌

[a3kov]

This code still generates a compiler warning because it refers to modules that may not be available.
The warning is present in the current version of PromEx too btw, so you could call this PR a bugfix (once you fix the warning of course).

[odarriba]

This code still generates a compiler warning because it refers to modules that may not be available. The warning is present in the current version of PromEx too btw, so you could call this PR a bugfix (once you fix the warning of course).

If you can test it again, now it should not emit any warning I think 🤔

[a3kov]

I'm using my fork already at least until this project starts accepting PRs again.
But yeah, declaring code conditionally should fix it.

[odarriba]

@akoutmos Any news on this? With this easy fix we will be solving compilation warnings on any new Phoenix app that uses Bandit by default 🙏