Kanban board (#8346)

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: jaqra <48099350+jaqra@users.noreply.github.com>
Co-authored-by: Kerry <flatline-studios@users.noreply.github.com>
Co-authored-by: Jaqra <jaqra@hotmail.com>
Co-authored-by: Kyle Evans <kevans91@users.noreply.github.com>
Co-authored-by: Tsakiridis Ilias <TsakiDev@users.noreply.github.com>
Co-authored-by: Ilias Tsakiridis <ilias.tsakiridis@outlook.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

models/fixtures/project_issue.yml

@@ -0,0 +1,23 @@
+-
+  id: 1
+  issue_id: 1
+  project_id: 1
+  project_board_id: 1
+
+-
+  id: 2
+  issue_id: 2
+  project_id: 1
+  project_board_id: 0 # no board assigned
+
+-
+  id: 3
+  issue_id: 3
+  project_id: 1
+  project_board_id: 2
+
+-
+  id: 4
+  issue_id: 5
+  project_id: 1
+  project_board_id: 3