Update config.yml

[Dargon789]

Summary by Sourcery

Configure a custom CircleCI executor and job for the project and wire it into a renamed workflow.

CI:

• Introduce a reusable Docker-based executor with authenticated access to Docker Hub using environment variables.
• Replace the sample 'say-hello' job with a project-specific job using the custom executor.
• Rename and update the CircleCI workflow to run the new project job instead of the example job.