Allow repositioning epics on epic boards

* allows moving epics between lists
* disables resorting of epics by position (this is done on server side)

ee/app/assets/javascripts/boards/boards_util.js

-import { sortBy } from 'lodash';
 import { FiltersInfo as FiltersInfoCE } from '~/boards/boards_util';
 import { getIdFromGraphQLId } from '~/graphql_shared/utils';
 import { urlParamsToObject } from '~/lib/utils/common_utils';
@@ -44,10 +43,9 @@ export function formatListEpics(listEpics) {
 
   const listData = listEpics.nodes.reduce((map, list) => {
     listItemsCount = list.epicsCount;
-    let sortedEpics = list.epics.edges.map((epicNode) => ({
+    const sortedEpics = list.epics.edges.map((epicNode) => ({
       ...epicNode.node,
     }));
-    sortedEpics = sortBy(sortedEpics, 'relativePosition');
 
     return {
       ...map,

ee/app/assets/javascripts/boards/graphql/epic_move_list.mutation.graphql

@@ -3,9 +3,18 @@ mutation EpicMoveList(
   $boardId: BoardsEpicBoardID!
   $fromListId: BoardsEpicListID!
   $toListId: BoardsEpicListID!
+  $moveAfterId: EpicID
+  $moveBeforeId: EpicID
 ) {
   epicMoveList(
-    input: { epicId: $epicId, boardId: $boardId, fromListId: $fromListId, toListId: $toListId }
+    input: {
+      epicId: $epicId
+      boardId: $boardId
+      fromListId: $fromListId
+      toListId: $toListId
+      moveAfterId: $moveAfterId
+      moveBeforeId: $moveBeforeId
+    }
   ) {
     errors
   }

ee/app/assets/javascripts/boards/stores/actions.js

@@ -405,6 +405,8 @@ export default {
           boardId: fullEpicBoardId(boardId),
           fromListId,
           toListId,
+          moveAfterId: moveAfterId ? fullEpicId(moveAfterId) : undefined,
+          moveBeforeId: moveBeforeId ? fullEpicId(moveBeforeId) : undefined,
         },
       })
       .then(({ data }) => {

ee/spec/features/epic_boards/epic_boards_spec.rb

@@ -87,14 +87,29 @@ RSpec.describe 'epic boards', :js do
       expect(find('.board:nth-child(3) .board-card')).to have_content(epic3.title)
     end
 
-    it 'moves epic between lists' do
-      expect(find('.board:nth-child(1)')).to have_content(epic3.title)
+    it 'moves to the bottom of another list' do
+      expect(find_board_list(1)).to have_content(epic3.title)
 
-      drag(list_from_index: 0, list_to_index: 1)
+      drag(list_from_index: 0, list_to_index: 1, to_index: 1)
       wait_for_all_requests
 
       expect(find_board_list(1)).not_to have_content(epic3.title)
-      expect(find_board_list(2)).to have_content(epic3.title)
+      page.within(find_board_list(2)) do
+        expect(all('.board-card')[1]).to have_content(epic3.title)
+      end
+    end
+
+    it 'moves to the top of another list' do
+      expect(find_board_list(1)).to have_content(epic3.title)
+
+      drag(list_from_index: 0, list_to_index: 1, to_index: 0)
+      wait_for_all_requests
+
+      expect(find_board_list(1)).not_to have_content(epic3.title)
+
+      page.within(find_board_list(2)) do
+        expect(all('.board-card')[0]).to have_content(epic3.title)
+      end
     end
 
     context 'lists' do