[8.x] Added assertRedirectContains

[Livijn]

This adds the ability to call assertRedirectContains() on the TestResponse. For example when using Cashier, one might use return Auth::user()->redirectToBillingPortal(); which redirects to a url like https://billing.stripe.com/session/_KOsvPyL7ZaTxYiyD8sHhfm4ZK6ewPJ8.

This is continuation from #39189

Before

$response = $this->get(route('checkout']))->assertRedirect();

$this->assertStringContainsString('https://checkout.stripe.com/', $response->headers->get('Location'));

After

$this->get(route('checkout']))
    ->assertRedirectContains('checkout.stripe.com');