[Certification] Defining Spec Requirements when running self certification tool.

With Self certification tool available for customers to certify their own platform/setup from 2.3.0-beta, it would be ideal to have a spec requirements section in our docs highlighting the infra parameters like number of nodes in the k8s cluster, number of vCPUs, total memory against the parallelisation value. 

However we don't need the exact numbers, touching upon the range of different params defined should do as well. 

This could prevent the customers from using an insufficient cluster in terms of infra against high parallelisation of tests.

(QE uses 9 node k8s cluster with 36vCPUs in total with 144GB memory.)