create URL checker

[hohwille]

For our epic #941 we have decided to do the implementation in Java what is way more maintainable compared to bash.
This story is about implementing the URL checker.
It shall be a simple component that takes an URL, performs an HTTP HEAD request to check if the URL is valid and returns a result that is either a success (200 OK) or an error (e.g. 404 Not Found).
The internal design should clarify if we need a structured result object containing the HTTP status code separated from the HTTP response message that could also contain details on an error such as 500.
The most important thing however is that we need to be able to determine if the result was a success or not very easily (e.g. result.isSuccess()).

[hohwille]

Done with PR #1042 (for #1009)