Feature/convop register provider request

### Description
A closer look at the ngsi9 convenience operation 'ContextEntitiesByEntityId' ( /ngsi9/contextEntities/{entityId} ) revealed that there was a problem with the response payload for unsupported METHODs (only GET and POST are supported). 
Check out the new function payloadWordGet(). This function will be useful for all the conv ops, in the <i>badVerbXXX</i> service routines.

### Testing and Code Coverage
A pretty thorough harness test has been added, while the unit test for this conv op was maintained at 100%