Merge branch 'jh-bulk_import_docs' into 'master'

Add class documentation for the bulk import models

See merge request gitlab-org/gitlab!45414

app/models/bulk_import.rb

 # frozen_string_literal: true
 
+# The BulkImport import model links together all the models required to for a
+# bulk import of groups and projects to a GitLab instance, and associates these
+# with the user that initiated the import.
 class BulkImport < ApplicationRecord
   belongs_to :user, optional: false
 

app/models/bulk_imports/configuration.rb

 # frozen_string_literal: true
 
+# Stores the authentication data required to access another GitLab instance on
+# behalf of a user, to import Groups and Projects directly from that instance.
 class BulkImports::Configuration < ApplicationRecord
   self.table_name = 'bulk_import_configurations'
 

app/models/bulk_imports/entity.rb

 # frozen_string_literal: true
 
+# The BulkImport::Entity represents a Group or Project that is going to be
+# imported during the bulk import process. An entity is nested under the a
+# parent group when it is not a top level group.
+#
+# A full bulk import entity structure might look like this, where the links are
+# parents:
+#
+#          **Before Import**              **After Import**
+#
+#             GroupEntity                      Group
+#              |      |                        |   |
+#     GroupEntity   ProjectEntity          Group   Project
+#          |                                 |
+#    ProjectEntity                        Project
+#
+# The tree structure of the entities will result in the same structure for the
+# imported Groups and Projects.
 class BulkImports::Entity < ApplicationRecord
   self.table_name = 'bulk_import_entities'
 
@@ -33,11 +50,17 @@ class BulkImports::Entity < ApplicationRecord
 
   def validate_imported_entity_type
     if group.present? && project_entity?
-      errors.add(:group, s_('BulkImport|expected an associated Project but has an associated Group'))
+      errors.add(
+        :group,
+        s_('BulkImport|expected an associated Project but has an associated Group')
+      )
     end
 
     if project.present? && group_entity?
-      errors.add(:project, s_('BulkImport|expected an associated Group but has an associated Project'))
+      errors.add(
+        :project,
+        s_('BulkImport|expected an associated Group but has an associated Project')
+      )
     end
   end
 end