Publish Docker images more frequently

[bcipriano]

Describe the enhancement Publish Docker images on every commit to master, to avoid the latest Docker images getting stale.

Additional context Currently, Docker images are only published when an official release is tagged. We try our best to do releases regularly but sometimes issues arise that delay releases, sometimes for months. This means that master can drift pretty far in front of the last published Docker image.

For users running entirely from a single release, this is not a problem. For users running entirely from master, with locally built Docker images, this is also not a problem.

However -- if users have a mixed environment this can cause issues. In particular a common setup is to have Cuebot/RQD images come from Docker and client-side code come from a local build. Our quickstarts in particular use this setup.

OpenCue version numbers are generated based on commit history -- major/minor version comes from VERSION.in, and patch version comes from the number of commits since VERSION.in was updated.

https://github.com/AcademySoftwareFoundation/OpenCue/blob/529d606c67012a6630ac34838eb626fe03b69871/ci/generate_version_number.sh#L50-L53

This means that all commits already have a version number assigned to them, regardless of whether that version has been tagged as an official release.

We should modify our CI pipeline so that commits to master trigger a Docker image publish at that version, and update the latest tag as well.