Support short reference to group entities from project entities

- add a direct project parent (group) to Banzai context
- if an epic is referenced from a direct descendant
  -> change epic to_reference to use short reference

doc/user/project/quick_actions.md

 # GitLab quick actions
 
-Quick actions are textual shortcuts for common actions on issues, epics, merge requests, 
+Quick actions are textual shortcuts for common actions on issues, epics, merge requests,
 and commits that are usually done by clicking buttons or dropdowns in GitLab's UI.
 You can enter these commands while creating a new issue or merge request, or
-in comments of issues, epics, merge requests, and commits. Each command should be 
+in comments of issues, epics, merge requests, and commits. Each command should be
 on a separate line in order to be properly detected and executed. Once executed,
 the commands are removed from the text body and not visible to anyone else.
 
@@ -70,7 +70,7 @@ The following quick actions are applicable for epics threads and description:
 |:---------------------------|:----------------------------------------|
 | `/tableflip <Comment>`     | Append the comment with `(╯°□°)╯︵ ┻━┻` |
 | `/shrug <Comment>`         | Append the comment with `¯\＿(ツ)＿/¯`  |
-| `/todo`                    | Add a todo                              | 
+| `/todo`                    | Add a todo                              |
 | `/done`                    | Mark todo as done                       |
 | `/subscribe`               | Subscribe                               |
 | `/unsubscribe`             | Unsubscribe                             |
@@ -80,4 +80,4 @@ The following quick actions are applicable for epics threads and description:
 | `/award :emoji:`           | Toggle emoji award                      |
 | `/label ~label1 ~label2`   | Add label(s)                            |
 | `/unlabel ~label1 ~label2` | Remove all or specific label(s)         |
-| `/relabel ~label1 ~label2` | Replace label                           |
+| `/relabel ~label1 ~label2` | Replace label                           |
\ No newline at end of file

lib/banzai/filter/epic_reference_filter.rb

@@ -9,6 +9,12 @@ module Banzai
       def self.object_class
         Epic
       end
+
+      private
+
+      def group
+        context[:group] || context[:project]&.group
+      end
     end
   end
 end

spec/models/concerns/cache_markdown_field_spec.rb

@@ -331,11 +331,12 @@ describe CacheMarkdownField do
     end
 
     context 'with a project' do
-      let(:thing) { thing_subclass(:project).new(foo: markdown, foo_html: html, project: :project_value) }
+      let(:project) { create(:project, group: create(:group)) }
+      let(:thing) { thing_subclass(:project).new(foo: markdown, foo_html: html, project: project) }
 
       it 'sets the project in the context' do
         is_expected.to have_key(:project)
-        expect(context[:project]).to eq(:project_value)
+        expect(context[:project]).to eq(project)
       end
 
       it 'invalidates the cache when project changes' do