Update makefile to explicit version on build as well as deploy

[bdelcamp]

Not sure what build process you use, but the latest version is never explicitly version tagged. So when this is updated to 4.6, I can't version lock at 4.5.4. I couldn't raise an issue on the repo, so I created a pull request to see if you could just explicitly tag images. Thanks!!!

[dereckson]

Issues -> That's because GitHub is a mirror of our repository hosted on a Phabricator instance -> issues can be seen at https://devcentral.nasqueron.org/tag/xmpp/ (with a part related to our own server deployment)

Release process -> it's configured as an automatic build on Docker Hub, reacting to tags, so what would be the most useful would be to push tags I guess, and it's a cool idea to use the Makefile for that, because it's often forgotten, let's add a git push origin --tags in release process.

Another idea -> we can also perhaps configure a Jenkins job (adding a Jenkinsfile to the repo) to "fix" tags when a commit reach master:

1. check if tag defined in VERSION exists
2. if not, create it to current commit and push it

That would avoid humans forgot that ;)

[dereckson]

(side comment: I've pushed a 4.5.4 tags by the way, so you can now lock it)

[dereckson]

By the way pin the version could be a good idea: https://discourse.igniterealtime.org/t/cant-enter-to-any-conference-room-on-spark-2-9-2-after-update-openfire-to-4-6/88974/5