CI: use Docker to build binaries for linux-arm64

[jesec]

Recently it comes to my attention that Github Actions image installs
experimental C++ standard library from an unsupported PPA, which
effectively breaks assumptions of binary compatibility for the OS
(in this case, Ubuntu 18.04+).

Unfortunately, as a result, the Github Actions environment can no
longer be trusted to compile proper binaries.

This change adds a Dockerfile that composes a proper Ubuntu 18.04
environment from official "ubuntu:bionic" image, and builds Node
binaries in it.

Refs: actions/runner-images#3376, actions/runner-images#3432, actions/runner-images#3459

[jesec]

I am also thinking about using Red Hat's llvm-toolset-rhel7, which has cross compiling capabilities and allows us to extend the compatibility of arm64 binaries to EL 7+ and Ubuntu 14.04+. However, I have some concerns about the binary compatibility between LLVM-made Node binaries and GCC-made (prebuilt) Node bindings.

edit: compiler alone is not enough. The image does not include a full cross-capable toolchain (arm64 headers/libs of C++ STL, etc.) unfortunately.

It is also an option to use CentOS / Oracle Linux 7 arm64 toolchain (Red Hat does not provide one for arm64), in line with the upstream and our x64 binaries (already using RHEL7 toolset). However, there is no cross toolchain, and as I explained in #124, we can't use emulation to build such a large project. We have to get a native arm64 machine for CI if we want to choose this option.

[robertsLando]

We have to get a native arm64 machine for CI if we want to choose this option.

I think that @leerob could ask to @vercel team if they could provide us an arm64 machine and setup a custom github runner.

Agree with all your ideas @jesec

[robertsLando]

LGTM. Hope the build time will not be too long now