Webhook notification action

[dkarlovi]

Q	A
Bug report?	no
Feature request?	yes
BC Break report?	no
RFC?	no

Pretty simple, a notification action which basically does this:

    public function apply($subject, NotificationRuleInterface $rule, array $configuration, array $params = []): void
    {
        $request = $this->messageFactory
            ->createRequest('POST', $configuration['url'])
            ->withHeader('Content-Type', 'application/json')
            ->withBody($this->streamFactory->createStream(json_encode($this->eventCreator->create($subject, $rule, $params), \JSON_THROW_ON_ERROR)))
        ;

        $this->client->sendRequest($request);
    }

[dpfaffenbauer]

@dkarlovi did you implement this? could you create a PR?

[dkarlovi]

I've implemented this on my project, would need to clean it up substantially to PR.