[FIX] doc: warnings when installing openacademy

* add _description to openacademy models
* add aria-label to kanban view
* many patches need to be rewritten to unfuzz them

closes odoo/odoo#27617

doc/howtos/backend/exercise-constraint-python

@@ -13,7 +13,7 @@ diff --git a/openacademy/models.py b/openacademy/models.py
  
  class Course(models.Model):
      _name = 'openacademy.course'
-@@ -56,3 +56,9 @@ class Session(models.Model):
+@@ -58,3 +58,9 @@ class Session(models.Model):
                      'message': "Increase seats or remove excess attendees",
                  },
              }