Evergreen containers

Hi,

When using `build.dockerfile` to create a development container and the Dockerfile is changed, a new container is built the next time it is opened. This makes sense to me.

When using `image` (or an equivalent `dockerComposeFile`) with a stable tag such as `latest` to create a development container, the image is not updated unless I do a `docker pull` or `docker-compose pull`. This surprises me.

Wouldn't it make sense to align these two so that you are always using a container based on the latest available image?