Add a new bot trigger for publishing prereleases from a PR #32412

Similar to @typescript-bot pack this, but will publish the packed release to a given tag on npm. For safety, it should forbid latest, next, and anything with release in the name.

For UX, I'm thinking @typescript bot release this as (name), so for example: @typescript bot release this as private-experiment, publishes the PR head as 3.6.0-privateexperiment.07152018 under the npm tag private-experiment.