Separate enterprise and non-enterprise tests so that outside contributions can run non-ee pipeline to completion

[pmalek]

Problem statement

Since we do not want to expose our secrets to outside world and make them available in CI workflows that run for outside contributions we need a mechanism/structure to adhere to, thanks to which we'll be able to separate enterprise and non-enterprise tests which in turn will allow us to make ee tests conditional (similarly to what has been done for go-kong: Kong/go-kong#247)