Add degraphql entity support

[mheap]

Add support for configuring degraphql entities using Deck.

https://docs.konghq.com/hub/kong-inc/degraphql/#3-configure-degraphql-routes-on-the-service

This may require changes in go-database-reconciler too

[mheap]

The KIC team recently added generic support using KongCustomEntity for schemas added by plugins. I recommend reading https://docs.konghq.com/kubernetes-ingress-controller/latest/guides/services/custom-entity/ to see how it works.

The important part is:

apiVersion: configuration.konghq.com/v1
kind: KongPlugin
metadata:
  namespace: default
  name: degraphql-example
plugin: degraphql
config:
  graphql_server_path: /v1/graphql
---
apiVersion: configuration.konghq.com/v1alpha1
kind: KongCustomEntity
metadata:
  namespace: default
  name: degraphql-route-example
spec:
  type: degraphql_routes
  fields:
    uri: "/contacts"
    query: "query{ contacts { name } }"
  controllerName: kong
  parentRef:
    group: "configuration.konghq.com"
    kind: "KongPlugin"
    name: "degraphql-example"

The spec.type field in the second config indicates the Kong entity name, and everything under fields is passed as the configuration.

This would translate to something similar to the following in deck:

plugin_entities:
  - plugin: my-degraphql-plugin
    entity: degraphql_routes
    fields:
      uri: "/contacts"
      query: "query{ contacts { name } }"
  - plugin: my-degraphql-plugin
    entity: degraphql_routes
    fields:
      uri: "/bookings"
      query: "query{ bookings { id, cost } }"
  - plugin: different-plugin
    entity: some-plugin-entity
    fields:
      foo: bar