Enable continuous deployment for SIT722 Task 9.3C - feature/sit722-9.3c-continuous-deployment

[clavillej]

SIT722 - Ontrack 9.3C - Cjeffrey

Automates production deployment after successful staging validation.

Changes:

• Enable CI tests for pull requests targeting main.
• Restrict staging deployment to eligible successful CI runs.
• Pass the image SHA between deployment and test workflows using artifacts.
• Verify staging image versions and rollout completion.
• Automatically deploy the tested images to production.
• Update the dashboard welcome message to demonstrate the deployed change.

Validation:

• Reviewed all five changed files using git diff.
• git diff --check reported no whitespace errors.
• CI and deployment results will be checked after creating and merging this pull request.