Add container support for server metrics recording.

[mojowill]

This includes detecting containerized environments and retrieving container-specific CPU and memory metrics. Test cases are added to verify functionality.

Bumped up against this when trying to use the Servers Recorder on a Laravel Cloud hosted application.

[timacdonald]

@mojowill, appreciate the PR.

Right now, I'm not wanting to put Laravel Cloud specifics into Pulse, but I agree this could be useful for others.

If you were keen, it would be great to package this functionality up into a package. That way, Pulse users could install your package and register the callables via the existing Pulse hooks, e.g.,

use Laravel\Pulse\Recorders\Servers;
use Your\Package\CpuCheck;
use Your\Package\MemoryCheck;

Servers::detectCpuUsing(new CpuCheck);
Servers::detectMemoryUsing(new MemoryCheck);

Those classes would be callable, e.g., use an __invoke method as the entry point to computing the CPU and memory usage, and contain the logic you have in the PR.

Thanks again.