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

## 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: https://github.com/Kong/go-kong/pull/247)

Start by reviewing the repository's existing Go integration-test layout and CI workflows, then compare the requested separation with the linked go-kong change. Define how enterprise tests can be made conditional while allowing non-enterprise tests to complete for outside contributions; done means the non-enterprise pipeline runs without exposed secrets.

Written by the indexing model from the issue text.