impr(cockpit): add help text to engine selection

related to #CAM-829
Merge branch 'master' of github.com:camunda/camunda-bpm-platform
Merge branch 'master' of github.com:camunda/camunda-bpm-platform
Merge branch 'master' of github.com:camunda/camunda-bpm-platform
chore(engine-IT): add spring PA EL testcase
Merge branch 'master' of github.com:camunda/camunda-bpm-platform