Remove schema prefix in ServersArePingable check

It would be very useful if there was an option per host for removing schema prefix (http://, https://), because when I want to use hostname from the config, like `config('app.url')`, it's very inconvenient to remove prefixes for each host.
Something like:
```php
\BeyondCode\SelfDiagnosis\Checks\ServersArePingable::class => [
'servers' => [
[
'host' => config('app.url'),
'port' => 80,
'timeout' => 1,
'remove_schema' => true,
],
]
]
```

@mpociot If you agree with the idea, I can implement and send PR

Start by inspecting the ServersArePingable check and how its per-host configuration is read. Verify that a host configured with an HTTP or HTTPS prefix can be used when the new option is enabled, while existing host configurations continue to work.

Written by the indexing model from the issue text.