License checking should additionally be part of the EWS

(Apologies if this is misfiled, but I don't see a better place...)

License checking being delayed until a contribution is ready to be merged can mean a rather long wait, followed by a build failure (= frustrating for the original contributor, also for everyone else who was integrating at the same time).

License checks should still be done at integration time, of course, but it would be nice to include an additional, advisory check into the sanity EWS.