Allow pinging and dryrunning the receptionist service

Current situation

There is no easy way to find out if the receptionist service is available or if a workflow is acceptable.

We can send a known invalid workflow to address the first point, but this pollute the logs and is a hack. There is no point to address the second point.

Desired outcome

A ping query parameter and a dryRun query parameter.

If ping is provided, no check is performed, the service simply returns a OK response with a Pong! content:

{
  "apiVersion":"v1",
  "code":200,
  "details":null,
  "kind":"Status",
  "message":"Pong!",
  "metadata":{},
  "reason":"OK",
  "status":"Success"
}

If dryRun is provided, all checks are provided, but the workflow is not sent to the eventbus. The possible responses are just like those without the dryRun query parameter.

In both cases the X-Processed-Query header is filled in the response.