Cancel in-progress deployment on new deploy

[cptnnemo9]

When a new deployment is triggered, any older queued or currently running deployment for the same service should be automatically canceled.

This is useful when multiple commits are pushed in quick succession. In that case, deploying the older commit is unnecessary(usually), and only the latest commit should be deployed.

Example:

• Commit A → deploy starts
• Commit B shortly after → new deploy triggered
• Deployment for Commit A is canceled
• Only Commit B is deployed