Add a headerWhitelist config property

[f-necas]

Hi there,

We wanted to know (and if you were interested) in a headerWhitelist property (or blacklist) to be able to remove some headers from the request.

Some servers are impacted by X-Forwarded-* header and send wrong response. Also, the proxy sends "Cookie" header and may be wrongly used.

WDYT @tdipisa ?

[tdipisa]

@f-necas thank you for opening this. Please give me some time to consider that. I will get back to you shortly. Thank you.

[tdipisa]

@f-necas I'm sorry. It could be definitely an interesting configuration option. Do you already have something to contribute for this? Let me know. Thank you for the issue anyway.