Allow to pass an existing request object in constructor

[ofabel]

The current implementation always creates the HTTP request from the superglobals:

public function __construct()
{
    if (null === $this->request) {
        $this->request = HttpRequest::createFromGlobals();
    }
}

But this is not always possible (e.g. when using RoadRunner). It's also an issue in combination with other frameworks (see #440).

With this pull request, users can pass their own Symfony HTTP request object in the constructor - if necessary.

Of course one could also extend the Request class and do the same. But this would also require extending the Server class.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.60%. Comparing base (a466a9b) to head (41acd14).

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #442   +/-   ##
=========================================
  Coverage     99.60%   99.60%           
  Complexity      362      362           
=========================================
  Files            20       20           
  Lines          1007     1008    +1     
=========================================
+ Hits           1003     1004    +1     
  Misses            4        4           

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