Upgrade Github Showcase Example

This example has old concepts from when the SW implementation was at the beginning. We need to change it to reflect the new updates, architecture, and integration with Knative that we have now.

Besides updating the component versions and verifying if the example still works, we need the following:

• Update the Kubernetes templates to deploy the example
• Update the documentation to reflect the changes
• Verify if the Knative Github Source still works as intended
• Add the example back to the examples pom, so it can return to the pipelines check