tagged releases fixed with version numbers

[stephenmoloney]

Issue:

Currently the images in the dockerhub are just divided by type, eg stable-alpine
but they are not pinned by version number, eg alpine-1.14 and stable-alpine.

The issue therefore is that stable-alpine is a moving target and some users might want access
to a fixed version such as alpine-1.14.

Proposed solution

Release unaltered images with pinned versions

[alessfg]

@stephenmoloney I've created new tags as suggested - tags now match the tags for the official NGINX Docker image. You can find a list of the new tags here https://hub.docker.com/r/nginxinc/nginx-unprivileged/tags/.

[stephenmoloney]

@alessfg thanks !