docker-template - push the image with :latest too, on tag event

Update our template to also push the image with :latest on tag event. We don't sign it.

This is useful for renovate, when renovate is using the docker datasource it will looks for labels in the latest stable image of the repo to determine some info (in our case the sourceUrl used to retrieve the release notes info)

https://docs.renovatebot.com/modules/datasource/docker/#table-of-values