fixed a bug in POST /v1/contextEntities

### Description
The type of the entity was not passed to the lower layers and thus not saved in the database.
It was lost.  The fix was more than easy, but as the case was not covered in functests, a new functest had to be added.

Fixes issue #684.

Ok, NTC.

However, I'd suggest to defer issue closing to @anabelengp can test the new version and check that everything is ok (instead of closing the issue just after PR merging as usual).