Support some generic tags of molecule docker image

[aravinder111]

Issue Type

• Feature request

Problem

1. latest tag of quay.io/ansible/molecule image points to an older version of molecule.

$ docker run --rm quay.io/ansible/molecule:latest molecule --version
molecule, version 2.20.0.0a3.dev12

2. Today there are specific version image tags in https://quay.io/repository/ansible/molecule?tab=tags, but there is are generic versions like v2 or v3

Desired Behavior

1. latest tag of quay.io/ansible/molecule image should point to latest release available.

2. Support docker image tags for major versions.
   For Example:

docker pull quay.io/ansible/molecule:v2
or
docker pull quay.io/ansible/molecule:2
-----
docker pull quay.io/ansible/molecule:v3
or
docker pull quay.io/ansible/molecule:3
-----
# latest should match latest release available 
docker pull quay.io/ansible/molecule:latest