Implement upload and get file endpoints for APIv4 (#5396)

* Implement POST /files endpoint for APIv4

* Implement GET /files/{file_id} endpoint for APIv4

.gitignore

@@ -71,6 +71,7 @@ web/sass-files/sass/.sass-cache/
 data/*
 webapp/data/*
 api/data/*
+api4/data/*
 
 enterprise