feat: publish dbc to npm

[amoeba]

Adds support for publishing dbc to npm by,

1. Adding a create_packages.js script and shell packages that can create npm packages for each platform
2. Integrating this into the release.yml workflow so we publish to npm automatically as part of a release

There are two options for shipping dbc on npm,

1. A single package with a postinstall script that detects the user's platform and downloads and installs dbc at install time
2. One package for each platform, with a wrapper package for the user to install

Option 1 is the only one supported by goreleaser but option 2 is better IMO because we ship the dbc binary in the npm package. This means installation isn't making an extra request to a separate origin and it also means the package can be installed with scripts disabled.

Closes #355

[amoeba]

I changed how the npm artifacts are built so as little as possible is checked into the repo. create_package.js now creates the entire file structure, including package.json. This is ready for another review.

[zeroshade]

LGTM, my only question is whether there is any ability to add a "snapshot" style dry-run path to the CI somehow (for example, we have --snapshot for goreleaser so that we can ensure via CI that we don't break the release process).

[amoeba]

I added a step that just creates the npm packages to the snapshot job in bcec6d5.

[amoeba]

I'm going to test the update to the snapshot job in a separate draft pr before merging just to make sure it works.

[amoeba]

Okay, the snapshot job now has a test that actually installs the wrapper package and makes sure the equivalent of dbc --version runs successfully. I'll merge this.