Support multi-package releases

[David Elner (delner)]

This pull request attempts to simplify the mechanics for multi-package release workflows by:

1. Reducing the number of jobs required to prepare a package (merge of configure and prepare)
2. The ability to produce/consume package manifests (JSON metadata that describes what's being released) in various actions.
3. Allow request-approval to enumerate multiple packages in its descriptions/messaging (via package manifest)
4. Add idempotent behavior when one package in a multi-package workflow fails (allow for self-healing/rerunning the same version without republishing existing versions)

In sum, this should make it easier to build and deploy release workflows for repositories that need to release multiple packages in a single workflow.

[David Elner (delner)]

This is a pre-requisite for braintrustdata/autoevals#204 and may also be beneficial for braintrustdata/braintrust-sdk-javascript#2216