Add http proxy options provisioning for gpg

[KozelAnatoliy]

I am tying to use cypress/factory as base image to build specific cypress and browsers combination for our project.

The image is build behind firewall and fails during gpg --batch --keyserver.ubuntu.com --recv-keys ... stage.
The problem can be fixed providing --keyserver-options "http-proxy=$HTTP_PROXY" to the gpg command but there is no exposed argument for that and gpg command itself does not honor HTTP_PROXY env variable.

[KozelAnatoliy]

Updating gpg.conf would also be a good option to resolve this problem.