Add EVS-BE test to merge request pipeline as manually triggered job

When fixing non-BE-to-EVS issues on a branch, it would come in handy to have the possibility of triggering the EVS-BE test in an MR pipeline. We could add it as a manually triggered job there, so it would not increase the runtime of general merge request pipelines, but can be used to check that the developed fix will indeed help. Currently, one needs to run the test either locally (using the conformance test package) or merge to main to get test results.