Add CI to run E2E tests

As https://gitlab.cern.ch/webservices/webframeworks-planning/issues/37 is still an ongoing project with this issue we want to introduce a simple CI that runs our tests for us every time code is pushed.

I suggest us using a temporary KUBECONFIG file that will live in the variables of the project which will allow us to run tests on a tmp cluster.

Steps to take:

• Add kubeconfig file to variables
• Find if there's a pre-built docker image with operator-sdk-cli
• Write CI with two new pipelines, first gotests second with operator-sdk tests