Add an action to update draft release notes

[dmikusa]

Summary

• Adds action draft-release which replaces update-draft-release-buildpack.sh
• Deprecates usage of update-draft-release-buildpack.sh, this will be removed in a future version
• Action takes the same inputs, release name, release id, release body and release tag name. It also takes a dry_run argument for testing. When set to anything, it will write the name/body files to STDOUT and skip calling gh, instead writing the command that would have been called. This is for testing purposes.
• Adds tests for all of the draft release behavior, including: sourcing information, loading remote buildpack info, and generating output from templates
• Adds workflows to generate and publish the action
• Modifies octo to use the action instead of the previous script. This should be a drop-in replacement, but if it breaks pipelines we retain the script so that you can switch back to it.

Use Cases

Remove shell scripts and replace with Go-based, testable actions.

Checklist

• I have viewed, signed, and submitted the Contributor License Agreement.
• I have linked issue(s) that this PR should close using keywords or the Github UI (See docs)
• I have added an integration test, if necessary.
• I have reviewed the styleguide for guidance on my code quality.
• I'm happy with the commit history on this PR (I have rebased/squashed as needed).