feat: Base classes for server and client http exceptions.

[Johannestegner]

Type of change

• New feature
• Bug fix
• Security patch
• Documentation update

Description

Adds two new base classes for Client and Server HTTP errors.
Will allow easier checks on reporting and similar:

if ($e instanceof HttpClientException) { 
  ...
}

// Rather than
if (($e instanceof HttpException) && ($e->getStatus() > 399 && $e->getStatus() < 500))  {
  ...
}