Refactor to a single Zuul filter

[apnicjim]

This is what I mean by 1 Zuul filter. It should remove the need for the error handler to untangle the framework exceptions. I've kept the refactoring to a minimum in order keep this PR clear, though I think there are more opportunities, e.g. pass the RDAPRequestPath instead of a Zuul context.

[tlm]

Cheers,

But this isn't going to work. Specifically Zuul has an error filter type that it relies on. I have had to disable and override the default one the spring injects.

Unless there is specific tangible improvement I don't think I am willing to invest any more time in this. Its very functional at the moment and conforms to what I consider the standard design pattern when using Zuul.

Focus at the moment is on testing.