how to query EmbeddedDocumentListField in the GraphQL

**Note: for support questions, please use stackoverflow**. This repository's issues are reserved for feature requests and bug reports.

* **What is the current behavior?**
EmbeddedDocumentListField can't be queried and I couldn't find anything in the documentation.
I get the following error `"Cannot query field \"candidateToolPairs\" on type \"Column\".",`

Code gist is available: https://gist.github.com/ahmad88me/d489b8aa87e71d24e28606e5b502ab28

``` # schema.py
class Column(MongoengineObjectType):
class Meta:
model = ColumnModel
interfaces = (Node,)
```
with the model class `Column` include `candidate_tool_pairs = EmbeddedDocumentListField(ToolCandidatePair)`

In the graphQL interface, all the field of the class Column loads successfully, but the field `candidate_tool_pairs` (I tried candidateToolPairs as well. Also nothing starts with candidate is suggested by the autocomplete).

Instead, I get the following error: `"Cannot query field \"candidateToolPairs\" on type \"Column\".",`

* **What is the expected behavior?**
To get the list candidateToolPairs

* **Please tell us about your environment:**
```Flask==1.1.2
Flask-GraphQL==2.0.1
graphene==2.1.8
graphene-mongo==0.2.13
graphql-core==2.3.2
graphql-relay==2.0.1
graphql-server-core==1.2.0
mongoengine==0.19.1
pymongo==3.11.0```

* **Other information** (e.g. detailed explanation, stacktraces, related issues, suggestions how to fix, links for us to have context, eg. stackoverflow)