Provide ocp version related variable files

[yussufsh]

We are going to share variable file for each version and ask user to use a particular file while installing a required OCP version. The default variables will only support latest stable release.
Eg:

ocp-4.9.tfvars
ocp-4.10.tfvars

The docs need to change to show how to run the terraform command, terraform apply -var-file var.tfvars -var-file ocp-4.9.tfvars..

These files should only contain limited variables required for installing a specific OCP version.