There are two repositories on docker hub. mfgroupwise/web, and mfgroupwise/webacc-ng. The first if for officially tested and released versions. It will generally be updated along with the major releases of the GroupWise code. You can see the release history on docker hub. /webacc-ng is updated far more frequently and is considered "tech preview" or "beta" releases. If your users need proxy access then go with /webacc-ng for now.
The great thing about docker is the /latest tag is assumed. As you are already aware, simply restarting the image it will automatically update if there is a newer version in either channel. Since restarts are pretty fast it might be easier to simply restart than take the time to look it up on docker hub.