Add functionality to allow running behind a reverse proxy with correct IP logging

[pr0ton11]

What

This adds the necessary configuration for Fiber to run behind reverse proxy and log the correct IP address of the caller

Why

Whenever someone is running this behind a reverse proxy, only the reverse proxies IP is logged. This is not very helpful for analytics.

How

• Added new configuration parameters (optional) to allow setting reverse proxy header and list of trusted proxies
• Added the necessary configuration for Fiber to utilize this configuration and return the proper IP when calling ctx.IP() according to the documentation.

Small performance overhead gets generated by utilizing EnableIPValidation but this is a good way to ensure not returning spoofed, invalid IPs

[ryanolee]

Thanks for raising this PR; will have a look this weekend! 👀
( I might add a new example in the examples dir with nginx configured just to confirm it works 🙌 )
I think the performance overhead is fine as you would have to set the option first anyway. Code looks good!

[ryanolee]

Awesome. Looks to work. Made a few minor changes in #5 to fix issues with config so that it would work and added an example to show it working with a trusted proxy configuration