feat: add new scaffolder action to send notifications

[drodil]

Hey, I just made a Pull Request!

Adds a new scaffolder backend module that adds support to send notifications from templates

:heavy_check_mark: Checklist

• [x] A changeset describing the change and affected packages. (more info)
• [ ] Added or updated documentation
• [x] Tests for new functionality and regression tests for bug fixes
• [ ] Screenshots attached (for UI changes)
• [x] All your commits have a Signed-off-by line in the message. (more info)

[backstage-goalie[bot]]

Changed Packages

Package Name	Package Path	Changeset Bump	Current Version
example-backend	packages/backend	none	v0.2.98-next.1
@backstage/plugin-scaffolder-backend-module-notifications	plugins/scaffolder-backend-module-notifications	patch	v0.0.0

[github-actions[bot]]

Uffizzi Cluster pr-24588 was deleted.

[github-actions[bot]]

Thank you for contributing to Backstage! The changes in this pull request will be part of the 1.27.0 release, scheduled for Tue, 14 May 2024.