Enable to trigger e2e tests for operator

What it does

Sylva is maintaining 5 operators. For some of them, e2e tests have been developed. The present MR is aiming at factorizing code by adding a test stage job for e2e tests. It calls `make e2e-test to execute e2e tests of an operator executed on a full k8s cluster (like kind)

Details

• The job is not triggered automatically, since it may be long
• By setting SET_DOCKER_HOST to true, a variable required to expose controller to a binary not run in k8s is set. See sylva-projects/sylva-elements/sylva-units-operator!314 (merged) for instance