Allow removal of prefix when proxying to another server (#630)

[nudejustin]

Adds a new set of properties to the proxy server settings that allow prefix url rewriting in order to resolve issue #630

[StefH]

please take a look at my comments

[nudejustin]

@StefH The CI linter was flagging the parser method as being too complex now after the changes you suggested above. I've refactored the code a bit further to hopefully make the flow easier to understand at the top level function level, whilst also introducing the change youn suggested in the more specific function. Let me know if you'd prefer this done in a different way than I approached it.