Document unpublish options for a botched release

Action item from [requiem/doc/postmortem475066](http://requiem/doc/postmortem475066).

In the `14.1.0-rc.0` tooling release, the process failed part way through leaving it in an inconsistent state. We considered unpublishing the packages on NPM that were released, but weren't fully sure of the implications and restrictions to doing so and decided to abandon the release instead and push new `14.1.0-rc.x` versions instead.

We should figure out what options are actually available for unpublishing, their implications and restrictions, and have a playbook entry in a caretaker doc about when and where unpublishing can be the right solution to a given problem. Alternatively we can decide that unpublishing is never a good idea and we should always just abandon a release and bump a patch, but that should be documented as well.