Add limit to epics requested from backend on Roadmap

ee/app/assets/javascripts/roadmap/queries/groupEpics.query.graphql

@@ -11,6 +11,7 @@ query groupEpics(
   $milestoneTitle: String = ""
   $confidential: Boolean
   $search: String = ""
+  $first: Int = 1001
 ) {
   group(fullPath: $fullPath) {
     id
@@ -25,6 +26,7 @@ query groupEpics(
       milestoneTitle: $milestoneTitle
       confidential: $confidential
       search: $search
+      first: $first
     ) {
       edges {
         node {

ee/app/assets/javascripts/roadmap/store/actions.js

@@ -45,6 +45,7 @@ const fetchGroupEpics = (
     variables = {
       ...variables,
       ...filterParams,
+      first: gon.roadmap_epics_limit + 1,
     };
   }