Create new docker image with CGO enabled

[maraino]

Description

We should add a new docker image where step-ca is built with CGO enabled (e.g. smallstep/step-ca-cgo).

This will allow users to create custom images to support a specific HSM just by inheriting this image and adding the necessary PKCS#11 modules and dependencies. For example, to add support to yubikey you might need to add yubihsm_pkcs11.so, yubihsm_pkcs11.conf, set the environment variable YUBIHSM_PKCS11_CONF, and add any necessary dependencies.

We also need to consider that step-ca images are based on alpine, with musl, instead of libc, but PKCS#11 modules might depend on libc, so we might want to change the base image to be based on Debian or Fedora.

[jschlyter]

https://github.com/kirei/smallstep-ca-hsm now contains Dockerfiles for CGO containers for Fedora, Debian and Alpine. Feel free to use any of these as input to this issue.

[maraino]

This was fixed a few weeks ago, and now we have smallstep/step-ca:hsm with the latest version of step-ca with CGO support.