Docker's website has pretty sweet automation that you can use to re-build your containers automatically when the base image changes.
What you describe isn't hard to achieve. Write a one-line cron job that gets the latest packages for your container's base, writes them to a file, commits it to Git, and pushes it. Then set up a Git webhook that runs a script you have to build your container with a new version and push that to a dev instance. Add some tests, and you have an entire CI/CD process with just one cron job and one Git webhook.
What you describe isn't hard to achieve. Write a one-line cron job that gets the latest packages for your container's base, writes them to a file, commits it to Git, and pushes it. Then set up a Git webhook that runs a script you have to build your container with a new version and push that to a dev instance. Add some tests, and you have an entire CI/CD process with just one cron job and one Git webhook.