[Suggestion] Allow setting Proxy for access in corporate networks

[insunaa]

I'll mirror the issue I created in the toolbx repo (containers/toolbox#1827)
Is your feature request related to a problem? Please describe.
Starting Distrobox from a corporate network that blocks internet access for any path that does not use corporate HTTP Proxies (such as Squid or any other type of HTTP proxy that inspects packets) is not trivially possible.

Describe the solution you'd like
I would love if Distrobox had a way to configure a HTTP proxy globally or per user which the init script would then use to configure that proxy for the package managers inside of the containers. For example in Ubuntu/Debian, adding a file /etc/apt/apt.conf.d/99-distroboxproxy containing:

Acquire::http::Proxy "http://username:password@yourproxyaddress:proxyport";
Acquire::https::Proxy "http://username:password@yourproxyaddress:proxyport";

Describe alternatives you've considered
For some container OS's it might be enough to have HTTPS_PROXY https_proxy HTTP_PROXY http_proxy NO_PROXY and no_proxy environment variables set.

I've used the Github search function to check for similar issues, but I didn't find any.