Add new field to edition links

In order for whitehall to publish document collections that contain
taxonomy_topic_email_override in their links, the schema.json needs to
contain the field, not just the links.json

Adding the field to base links and regenerating the schemas only added
it to links.json, so when trying to publish we are seeing schema validation
errors:
'#/links' contains additional properties [\"taxonomy_topic_email_override\"] outside of the schema when none are allowed

Follows original PR: #2440

content_schemas/dist/formats/document_collection/publisher_v2/schema.json

@@ -89,6 +89,11 @@
         "related_policies": {
           "$ref": "#/definitions/guid_list"
         },
+        "taxonomy_topic_email_override": {
+          "description": "The taxonomy topic that email subscriptions for this document collection should go to - only for document collections converted from specialist topics",
+          "$ref": "#/definitions/guid_list",
+          "maxItems": 1
+        },
         "topical_events": {
           "$ref": "#/definitions/guid_list"
         },

content_schemas/formats/document_collection.jsonnet

@@ -69,6 +69,10 @@
   },
   edition_links: (import "shared/whitehall_edition_links.jsonnet") + {
     documents: "",
+    taxonomy_topic_email_override: {
+        description: "The taxonomy topic that email subscriptions for this document collection should go to - only for document collections converted from specialist topics",
+        maxItems: 1
+    },
   },
   links: (import "shared/base_links.jsonnet") + {
     government: {