Add support for x_forwarded_for

[Berserkir-Wolf]

Is your feature request related to a problem? Please describe.
When using a reverse proxy, kapowarr logs all requests as coming from the proxy.
2023-07-24T04:29:16.314292000Z [2023-07-24 16:29:16][waitress-0][INFO] Login attempt successful from 192.168.10.21

Describe the solution you'd like
I'd like an option in settings to enable reverse proxy support.
Enabling this could then activate the option for a baseurl (since that's pretty much the only reason to use one), and set the server process to listen for the x_forwarded_for header, which would pass information through so that the log would show the login attempt source correctly (provided the proxy is setting it correctly).

[Casvt]

I've never used proxies so I don't have much experience with them (I barely know how they even work). Searching StackOverflow, all solutions search for the HTTP_X_FORWARDED_FOR header. Is that the same as the X_FORWARDED_FOR header you give? Or would I need to check for both headers? How many "variances" are there of this header that I should be searching for?

[Berserkir-Wolf]

HTTP_X_FORWARDED_FOR is the proper name for it - should be using that.