E2E tests: use a unique set of configs

[bpedersen2]

Currently ,we have a few different e2e test configurations, and we should strive to get a unique set a one location.

currently (for github): the FE e2e test uses a ready-made backend container.

the BE e2e builds a fresh FE image from FE master.

And then we have differerent cypress configs lying around, some of which are not really used (at least in the github workflows).