Adds workflow to generate draft release notes and reformat old release notes

[ftianli-amzn]

Issue #, if available:

Description of changes:

• Add a config file to organize all labeled PRs and place under headers in the release notes, in ascending order based on the date they were merged into master.
• Add a workflow to create draft release notes under ‘Releases’ tab in GitHub, which uses the config file to format the notes body.
• Reformat old release notes to meet the unified standard.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.