docs: update release docs to reflect new tooling
docs: update release docs to reflect new tooling

Release tooling was updated in #2447 to use dev-infra's unified system. The actual documentation was mostly copied from the existing [Angular CLI release docs](https://github.com/angular/angular-cli/blob/e0a1a94e79a3b0a5ec03bb41c70e8f8674557c10/docs/process/release.md), with the key difference being that releases and published as necessary rather than every week.

angular/universal,angular/universal,angular/universal,angular/universal