Support HTTP authentication for gem servers #543
Description
Today, rv ci install gems from multiple servers successfully, but does not support authentication. Most private gem servers, either for internal gems or for paid gems, require HTTP authentication.
Bundler handles HTTP authentication by reading from its config, which can be a file or an env var. For example, here is avohq.io's documentation about how to install the paid Avo gems with authentication to their gem server: https://docs.avohq.io/3.0/gem-server-authentication.html.
This feature will be complete when rv can install gems from servers that require authentication. We may want to simply read Bundler's config to get the auth information, but this could also be a chance to start building out our own rv-specific config to hold things like auth secrets.