[9.x] Remove TrustHosts reliance on config helper

[axlon]

Redo of #39293.

This PR removes the TrustHosts middleware's reliance on the config() helper, this achieves two things:

• Developers can now unit test their application's implementation more easily, because they can simply mock the application instance this middleware receives through it's constructor
• If a developer were to extend Illuminate\Contracts\Foundation\Application::environment() for some reason, the middleware would now take that into account