Expose group_id attribute of export in API response

doc/api/vulnerability_exports.md

@@ -51,6 +51,7 @@ Example response:
   "id": 2,
   "created_at": "2020-03-30T09:35:38.746Z",
   "project_id": 1,
+  "group_id": null,
   "format": "csv",
   "status": "created",
   "started_at": null,
@@ -96,6 +97,7 @@ Example response:
   "id": 2,
   "created_at": "2020-03-30T09:35:38.746Z",
   "project_id": null,
+  "group_id": 1,
   "format": "csv",
   "status": "created",
   "started_at": null,
@@ -128,6 +130,7 @@ Example response:
   "id": 2,
   "created_at": "2020-03-30T09:35:38.746Z",
   "project_id": null,
+  "group_id": null,
   "format": "csv",
   "status": "created",
   "started_at": null,
@@ -164,6 +167,7 @@ Example response:
   "id": 2,
   "created_at": "2020-03-30T09:35:38.746Z",
   "project_id": 1,
+  "group_id": null,
   "format": "csv",
   "status": "finished",
   "started_at": "2020-03-30T09:36:54.469Z",

ee/lib/ee/api/entities/vulnerability_export.rb

@@ -9,6 +9,7 @@ module EE
         expose :id
         expose :created_at
         expose :project_id
+        expose :group_id
         expose :format
         expose :status
         expose :started_at

ee/spec/fixtures/api/schemas/public_api/v4/vulnerability_export.json

@@ -4,6 +4,7 @@
     "id",
     "created_at",
     "project_id",
+    "group_id",
     "format",
     "status",
     "started_at",
@@ -13,7 +14,8 @@
   "properties" : {
     "id": { "type": "integer" },
     "created_at": { "type": "date" },
-    "project_id": { "type": "integer" },
+    "project_id": { "type": ["integer", "null"] },
+    "group_id": { "type": ["integer", "null"] },
     "format": {
       "type": "string",
       "enum": ["csv"]

ee/spec/lib/ee/api/entities/vulnerability_export_spec.rb

@@ -14,6 +14,7 @@ describe ::EE::API::Entities::VulnerabilityExport do
       expect(subject[:id]).to eq(vulnerability_export.id)
       expect(subject[:created_at]).to eq(vulnerability_export.created_at)
       expect(subject[:project_id]).to eq(vulnerability_export.project_id)
+      expect(subject[:group_id]).to eq(vulnerability_export.group_id)
       expect(subject[:format]).to eq(vulnerability_export.format)
       expect(subject[:status]).to eq(vulnerability_export.status)
       expect(subject[:started_at]).to eq(vulnerability_export.started_at)