Add multi-stage docker file for CI image

[scinos]

Changes proposed in this Pull Request

Adds a new Dockerfile used to generate an image that will be used to run CI tests in TeamCity (see https://github.com/Automattic/wp-calypso/pull/45399/files#diff-e9c4033904a319e2d4b3dd1f864d1966R71).

This CI image is like node:12.18.0 with:

• Extra env options to configure the cache and max memory
• /calypso/.nvm with a nvm cache for faster Node installation
• /calypso/.cache/yarn with yarn cache for faster dependency installation
• /calypso/.cache/* with all webpack caches (babel, terser...) for faster compilations

Testing instructions

Checkout the branch and run ./bin/build-docker.sh foo (it will take a while, ~30m in my machine). You should end up with two new docker images, you can see them with docker image ls:

REPOSITORY         TAG                                               IMAGE ID            CREATED             SIZE
XXX/calypso/ci     foo                                               1fa1b89c3a1b        3 minutes ago       2.25GB
XXX/calypso/base   foo                                               af7d28124568        7 minutes ago       3.78GB

To check the content of the cache, run docker run --rm -ti --entrypoint /bin/sh XXX/calypso/ci:foo -c "ls -la /calypso/.cache"

[matticbot]

Test live: https://calypso.live/?branch=add/docker-base-image

[matticbot]

This PR does not affect the size of JS and CSS bundles shipped to the user's browser.

Generated by performance advisor bot at iscalypsofastyet.com.

[jsnajdr]

👍

[wp-desktop]

WordPress Desktop CI Failure for job "wp-desktop-mac".

@scinos please inspect this job's build steps for breaking changes at this link. For temporal failures, you may try to "Rerun Workflow from Failed".

Please also ensure this branch is rebased off latest Calypso.