Automate release branch creation

We need to perform the following tasks every time we create a release-*.* branch:

1. TypeScript creates a branch from master on GitHub.
2. TypeScript updates the version on that branch to beta.
   1. Update package.json
   2. Update src/compiler/corePublic.ts
3. TypeScript LKGs the branch.
4. SDK script is updated to sync from that branch.

We should find a way to do all of this “at once”.

[weswigham]

There is now a @typescript-bot create release-X.Y task that can be used in issues. Ideally, it should be used in a release tracking issue (where anything to do pertaining to the upcoming release process can be collected).

I can prepare tasks for the other common release branch activities, like syncing with master (for pre-RC), doing an LKG (if a cherry-pick-and-LKG command on a PR is insufficient), changing the release tag+version (from 0-beta to 0-rc to .1, to .2 and beyond), and, hopefully, triggering the final publish task.

With all that in place, all we should need is appropriate triggers for the VS SDK builds, right?

[uniqueiniquity]

I think the tag happens after all of this - there still may be changes in the release branch before the beta tag is created