Allow trusted proxies to be configured

[acelaya]

Summary

#2351 highlighted the fact that a change in akrabat/ip-address-middleware made Shlink stop detecting the visitor's IP address when using more than one reverse proxy.

That was temporarily solved with a workaround, but we should allow people configure a list of trusted proxies, and disable the workaround in that case.

Use case

Support Shlink instances that are served behind multiple reverse proxies, and continue detecting the visitor's IP address without the risk of a side effect or regression, introduced by the workaround that reverses the list of IPs in X-Forwarded-For.