Respond with offending source/target for `max_matrix_distance` loki error

As discussed in https://github.com/valhalla/valhalla/issues/3898#issuecomment-1377637254, we don't want to be too lenient on clients sending matrices which exceed the distance limit on one or more pairs.

However, we could at least respond with the source/target index which triggered the exception. Of course it could be multiple source/target pairs, but I'd not enter that complication. In worst case, the client will fail multiple times in a row, it doesn't matter so much for server performance.