For each pull request, it triggers a job consists of 'node.js version x
architecture' matrix.
When a tag is pushed, it creates a release idempotently, and publishes
artifacts to the release.

The versions of node.js and npm packages are selected from package
management. This is because node.js official distribution does not
(yet) offer FreeBSD binaries and `nvm` spends too much time compiling
node.js and npm from source.

`pkg` does not support installation of old version of packages with
`pkg-install` command, so the `pkg-add` approach has been elected to
install older node.js. For that matter, the exact version of node.js
and npm packages are resolved using pattern matching.

`cbsd` is used to create an i386 jail environment.

Co-authored-by: Oleg Ginzburg <olevole@olevole.ru>

In FreeBSD VM hosted on Google GCE, with `pkg search` command, it fails
to retrieve the latest list even after `pkg update -f` with `latest`
repository selected (checked with `pkg -vv search`). There seems to be
some caching mechanism involved, which I couldn't find a way to avoid.