Add a Docker image tag for the latest versioned release

[UlyssesZh]

Currently there is only one moving tag: latest points to the latest built Docker image. However, I would like the project to have two moving tags: one points to the latest built Docker image, and the other points to the latest Docker image built on a versioned release. Conventionally, they are named master and latest respectively.

[knu]

Thanks for the suggestion. I agree that separating the two moving tags makes sense, and I have opened #3801 to track the change. I will explain the background and release policy there, so I am closing this discussion in favor of the issue.