(TK-33) Add redirect support to proxying

This PR adds proper redirect support to proxying in the Jetty9 service. 
Yes, I understand that a correct implementation is not trivial (I'd expect that being implemented in the jetty's ProxyServlet already but apparently it's not there?). However, if we want to start experimenting with a simplified approach, please add at least the per-proxy setting that I'd set to 'false' for the legacy PE Console apps proxy (I'm afraid there are also redirects that should get back to the browser). And I'd agree with setting it to false by default, which is what the ProxyServlet does:

```
// Redirects must be proxied as is, not followed
client.setFollowRedirects(false);
```