feat: add ghcr image publishing

[MarceloRobert]

Adds an automatic github action to publish docker images to github container registry (ghcr)

These changes were already tested on my personal fork and can be seen here: https://github.com/MarceloRobert?tab=packages
You can also check the actions on my fork to see the last run of the CI.

Some changes will still be made, because the proxy-named image is just nginx and doesn't need to be updated every commit, and the dashboard-named image just builds the frontend and sends the static files to a volume.
Also, I'm still waiting on the other images, for the ingester and process_pending_aggregations.

External resources and references

• https://www.youtube.com/watch?v=RgZyX-e6W9E
• https://www.youtube.com/watch?v=eBs97F6b5YQ
• https://docs.github.com/en/packages/working-with-a-github-packages-registry/working-with-the-container-registry
• https://docs.github.com/en/packages/managing-github-packages-using-github-actions-workflows/publishing-and-installing-a-package-with-github-actions
• https://docs.github.com/en/actions/tutorials/authenticate-with-github_token#using-the-github_token-in-a-workflow
• https://stackoverflow.com/questions/69014742/github-denied-permission-denied-write-package

Closes #1739