Define process and tooling for creating a new NPM package

[dgp1130]

Action item from requiem/doc/postmortem475066.

The process for adding a new NPM package with our current release tooling is not documented or completely thought through right now. We should define that process and updating tooling to do whatever it can reasonably do automatically. Any other gaps should be documented so we don't forget how to apply the process in the future.

It the postmortem it's mentioned that using an NPM organization for @angular might be enough for new packages to "just work" without any special changes. That might be the ideal fix, though I'm not sure what blockers we have for that effort.