Add migrations for change notice content.

Closes #3481266

To test:

• migrate the files drupalorg_migrate_changenotice_upload_files, drupalorg_migrate_changenotice_upload_media_documents, drupalorg_migrate_changenotice_upload_media_images
• migrate the change notice nodes drupalorg_migrate_changenotice
• verify fields have been filled out appropriately

migrations/drupalorg_migrate_changenotice.yml

+id: drupalorg_migrate_changenotice
+label: 'Drupal.org Change Record'
+migration_group: drupalorg_migrate
+# Commenting out the below will require the d7_file migration.
+#migration_tags:
+#  - Drupal 7
+#  - Content
+
+#deriver: Drupal\node\Plugin\migrate\D7NodeDeriver
+source:
+  plugin: d7_node
+  batch_size: 1000
+  node_type: changenotice
+
+destination:
+  plugin: entity:node
+
+process:
+  type:
+    plugin: default_value
+    default_value: changenotice
+  langcode:
+    plugin: default_value
+    source: language
+    default_value: "und"
+  title: title
+  uid:
+    plugin: migration_lookup
+    migration: drupalorg_migrate_users
+    source: node_uid
+  status: status
+  created: created
+  changed: changed
+  promote: promote
+  sticky: sticky
+
+  field_change_record_status: field_change_record_status
+  field_change_to_branch: field_change_to_branch
+  field_change_to: field_change_to
+  field_issue_links: field_issue_links
+  field_description: field_description
+  field_impacts: field_impacts
+  field_projects:
+    plugin: sub_process
+    source: field_projects
+    process:
+      target_id:
+        plugin: migration_lookup
+        migration:
+          - drupalorg_migrate_project_module
+          - drupalorg_migrate_project_theme
+          - drupalorg_migrate_project_distribution
+          - drupalorg_migrate_project_drupalorg
+          - drupalorg_migrate_project_release
+          - drupalorg_migrate_project_theme_engine
+          - drupalorg_migrate_project_core
+        source: target_id
+        no_stub: true
+  upload:
+    plugin: sub_process
+    source: upload
+    process:
+      target_id:
+        plugin: migration_lookup
+        migration:
+          - drupalorg_migrate_changenotice_upload_media_images
+          - drupalorg_migrate_changenotice_upload_media_documents
+        source: fid
+
+migration_dependencies:
+  optional:
+    - drupalorg_migrate_users
+    - drupalorg_migrate_changenotice_upload_media_documents
+    - drupalorg_migrate_changenotice_upload_media_images
+    - drupalorg_migrate_project_module
+    - drupalorg_migrate_project_theme
+    - drupalorg_migrate_project_distribution
+    - drupalorg_migrate_project_drupalorg
+    - drupalorg_migrate_project_release
+    - drupalorg_migrate_project_theme_engine
+    - drupalorg_migrate_project_core
+
+dependencies:
+  enforced:
+    module:
+      - drupalorg_migrate