Clarify RHEL and podman versions in 3scale supported configuration

In 3scale Supported Configurations, The supported RHEL, Docker and Podman versions of self-managed APIcast is described like this:

7.0 (RHEL) + 1.13.1 (Docker)
8.0 (RHEL) + 1.0.0 (Podman)

It leads to misunderstanding. In regard to RHEL 7, the version should be "7.x" or "7.x (latest version)". 7.0 is not recommended. The same applies to RHEL 8 and Podman. Regarding Docker, RHEL 7 provides 1.13.1 for a long time. So the version looks reasonable.