Add "v2" and "2" tags to dockerhub releases

[vini-nu]

Welcome!

• [X] Yes, I've searched similar issues on GitHub and didn't find any.
• [X] Yes, I've searched similar issues on the Traefik community forum and didn't find any.

What did you expect to see?

I expected that docker pull traefik:v2 will not result in not existing image.

I use traefik in docker swarm and watchtower to automatically update. I don't want to use latest tag, in case v3 is released.

[LorneCash]

I agree, can we please get this?

[dumbasPL]

v3 and 3 as well please

[MortenCB]

This would be very helpful to keep it at latest version 2 and not upgrade to version 3 before I'm ready to do a lot of config changes. Please add a latest version 2 tag, so I don't have to manually keep an eye on which is the latest and change the version manually.