added rustls dangerous_configuration feature

[simp4t7]

Hi, I was having trouble connecting to docker running in minikube and figured that it's because rustls cannot handle ip addresses as hostnames without this feature. This worked as a pretty quick and easy fix. Thanks.

[fussybeaver]

Thanks for figuring this out.. According to the rustls docs:

this feature enables a dangerous() method on ClientConfig and ServerConfig that allows setting inadvisable options

I guess we don't want this enabled by default, so we'll need to feature flag this option in Bollard too.

[simp4t7]

Cool, thanks.

I think it might not be 'dangerous' if there's no user access to the Config.

But no harm in making it a feature anyways.

[fussybeaver]

Hmm.. I think you're right, let's just merge this.