Add upgrade_d7_file_private content migration

Copied from ref_migrations folder

drupal10/web/modules/custom/tag1_migration/migrations/upgrade_d7_file_private.yml

@@ -0,0 +1,65 @@
+uuid: a2400a4c-970d-436b-9302-fdf6c159d947
+langcode: en
+status: true
+dependencies: {  }
+id: upgrade_d7_file_private
+class: Drupal\migrate\Plugin\Migration
+field_plugin_method: null
+cck_plugin_method: null
+migration_tags:
+  - 'Drupal 7'
+  - Content
+migration_group: migrate_drupal_7
+label: 'Private files'
+source:
+  plugin: d7_file
+  scheme: private
+  constants:
+    source_base_path: 'http://ddev-migration-drupal7-web/'
+process:
+  fid:
+    -
+      plugin: get
+      source: fid
+  filename:
+    -
+      plugin: get
+      source: filename
+  source_full_path:
+    -
+      plugin: concat
+      delimiter: /
+      source:
+        - constants/source_base_path
+        - filepath
+  uri:
+    -
+      plugin: file_copy
+      source:
+        - '@source_full_path'
+        - uri
+  filemime:
+    -
+      plugin: get
+      source: filemime
+  status:
+    -
+      plugin: get
+      source: status
+  created:
+    -
+      plugin: get
+      source: timestamp
+  changed:
+    -
+      plugin: get
+      source: timestamp
+  uid:
+    -
+      plugin: get
+      source: uid
+destination:
+  plugin: 'entity:file'
+migration_dependencies:
+  required: {  }
+  optional: {  }