Add descriptions for EpicStateEnum

Changelog: changed
EE: true

.rubocop_manual_todo.yml

@@ -13,7 +13,6 @@
 # WIP See https://gitlab.com/gitlab-org/gitlab/-/issues/322903
 Graphql/Descriptions:
   Exclude:
-    - 'ee/app/graphql/types/epic_state_enum.rb'
     - 'ee/app/graphql/types/health_status_enum.rb'
     - 'ee/app/graphql/types/iteration_state_enum.rb'
     - 'ee/app/graphql/types/requirements_management/requirement_state_enum.rb'

doc/api/graphql/reference/index.md

@@ -14245,9 +14245,9 @@ State of an epic.
 
 | Value | Description |
 | ----- | ----------- |
-| <a id="epicstateall"></a>`all` |  |
-| <a id="epicstateclosed"></a>`closed` |  |
-| <a id="epicstateopened"></a>`opened` |  |
+| <a id="epicstateall"></a>`all` | All epics. |
+| <a id="epicstateclosed"></a>`closed` | Closed epics. |
+| <a id="epicstateopened"></a>`opened` | Open epics. |
 
 ### `EpicStateEvent`
 

ee/app/graphql/types/epic_state_enum.rb

@@ -5,8 +5,8 @@ module Types
     graphql_name 'EpicState'
     description 'State of an epic'
 
-    value 'all'
-    value 'opened'
-    value 'closed'
+    value 'all', description: 'All epics.'
+    value 'opened', description: 'Open epics.'
+    value 'closed', description: 'Closed epics.'
   end
 end