Adding more artifacts into Interrogate doesn't work

Hello,

I wanted to add some artifacts into Interrogate so that when new client enrolls it will be interrogated for slightly more info than what the default interrogate asks for. I looked at `grr/config/artifacts.py` and found out that this should be possible fairly easily with options provided by this config definitions. So I tried to add those artifacts i want as part of interrogate to both (one at a time) `Artifacts.knowledge_base_additions` and `Artifacts.interrogate_store_in_aff4_additions` but neither works.

When i add them to the `interrogate_store_in_aff4_additions` then i get following errors:

```
Traceback (most recent call last):
File "/usr/local/grr/grr/server/flow_runner.py", line 589, in RunStateMethod
direct_response=direct_response, request=request, responses=responses)
File "/usr/local/grr/grr/server/flow.py", line 301, in Decorated
res = f(*args[:f.func_code.co_argcount])
File "/usr/local/grr/grr/server/flows/general/collectors.py", line 617, in ProcessCollected
aff4_output_map, output_collection_map)
File "/usr/local/grr/grr/server/flows/general/collectors.py", line 776, in _ParseResponses
aff4_output_map)
File "/usr/local/grr/grr/server/flows/general/collectors.py", line 823, in _WriteResultToMappedAFF4Location
self.GetAFF4PathForArtifactResponses(result_type))
File "/usr/local/grr/grr/server/flows/general/collectors.py", line 873, in GetAFF4PathForArtifactResponses
(output_type, artifact.GRRArtifactMappings.rdf_map.keys()))
ArtifactProcessingError: No defined RDF type for ExecuteResponse. See the description for the store_results_in_aff4 option, you probably want it set to false. Supported types are: [\'Volume\', \'HardwareInfo\', \'SoftwarePackage\']
```
where `ExecuteResponse` is different for different artifacts (sometimes i get `Dict` etc...).

When i add them to the `knowledge_base_additions` list then the whole GRR will get broken while grr_worker is cycling incredibly fast in something along following lines:

Did i misunderstand those config options and they are in fact not for adding artifacts into interrogate process or is there something else wrong? Those artifacts I am adding are working perfectly fine outside interrogate (when called normally by ArtifactCollector flow).

Thanks for any input!