Added support for capturing Environment Variables

[phillip-haydon]

New settings to enable capturing environment variables.

builder.Services.AddRaygun(builder.Configuration, settings =>
{
  settings.EnvironmentVariables.Add("USER*");
  settings.EnvironmentVariables.Add("POSH_*");
});

Can do:

• Exact Match: PATH
• Starts With: POSH_*
• Ends With: *_VALUE
• Contains: *_banana_*

If you enter * only it will return nothing as we don't want to capture everything, variables should be opt-in and explicit, not capture everything and potentially leak sensitive data by mistake.