Add search filter to issue boards resolver

This filter is needed on issue boards page so
we need to support it also when listing board epics.

doc/api/graphql/reference/gitlab_schema.graphql

@@ -1174,6 +1174,11 @@ input BoardEpicIssueInput {
   """
   releaseTag: String
 
+  """
+  Search query for issue title or description
+  """
+  search: String
+
   """
   Filter by weight
   """

doc/api/graphql/reference/gitlab_schema.json

@@ -3144,6 +3144,16 @@
                 "ofType": null
               },
               "defaultValue": null
+            },
+            {
+              "name": "search",
+              "description": "Search query for issue title or description",
+              "type": {
+                "kind": "SCALAR",
+                "name": "String",
+                "ofType": null
+              },
+              "defaultValue": null
             }
           ],
           "interfaces": null,

ee/app/graphql/types/board_epic_issue_input_type.rb

@@ -45,6 +45,10 @@ module Types
     argument :not, Types::NegatedBoardEpicIssueInputType,
              required: false,
              description: 'List of negated params. Warning: this argument is experimental and a subject to change in future'
+
+    argument :search, GraphQL::STRING_TYPE,
+             required: false,
+             description: 'Search query for issue title or description'
   end
   # rubocop: enable Graphql/AuthorizeTypes
 end

ee/spec/graphql/resolvers/board_groupings/epics_resolvers_spec.rb

@@ -78,6 +78,13 @@ RSpec.describe Resolvers::BoardGroupings::EpicsResolver do
         expect(result).to match_array([epic1])
       end
 
+      it 'finds only epics for issues matching search param' do
+        result = resolve_board_epics(
+          group_board, { issue_filters: { search: issue1.title } })
+
+        expect(result).to match_array([epic1])
+      end
+
       it 'accepts negated issue params' do
         expect(Boards::Issues::ListService).to receive(:new).with(
           group_board.resource_parent,

ee/spec/graphql/types/board_epic_issue_input_type_spec.rb

@@ -7,7 +7,7 @@ RSpec.describe GitlabSchema.types['BoardEpicIssueInput'] do
 
   it 'exposes negated issue arguments' do
     allowed_args = %w(labelName milestoneTitle assigneeUsername authorUsername
-                      releaseTag epicId myReactionEmoji weight not)
+                      releaseTag epicId myReactionEmoji weight not search)
 
     expect(described_class.arguments.keys).to match_array(allowed_args)
     expect(described_class.arguments['not'].type).to eq(Types::NegatedBoardEpicIssueInputType)