Provide a way to set BetterErrors::Middleware.allow_ip!

[iJackUA]

Whey you run Hanami app inside Docker/Vagrant container (in dev env)
you request end up "as being from external REMOTE_ADDR" and BetterErrors does not show itself for security reasons.
We need a way to setup this option, for example:

BetterErrors::Middleware.allow_ip! '172.18.0.0/16'

Maybe it should be an ENV var available?
Like HANAMI_WEBCONSOLE_TRUSTED_IP ?

Details: https://github.com/charliesome/better_errors/wiki/Allowing-access-to-the-console

[jodosha]

@iJackUA Thanks for reporting this. I'd love to hear your opinion here: hanami/hanami#930

It's a ticket to solve the root problem (plugins that can accept settings). It would solve the allowed IPs problem as well.

Thanks in advance.