requests: Make more graphql friendly

[Tony Narlock]

django silk: 5.0.1

Limitation

Consider a graphene view at /api/graphql-endpoint: Requests to individual queries will show up the same, even though the request object would be able to have a query name parsed out.

Potential solution

Two things are needed:

1. An optional custom label field for Request model

   If there was a label / title to give requests for what to show in /silk/requests/ instead of request.path

2. An optional callback in RequestModelFactory.construct_request_model() to customize the contents of models.Request.

   It will have accessed to to the django HttpRequest via self.request to fetch any necessary metadata and write a label