uploads: mark old columns as ignored.

Mark old columns as ignored in preparation for dropping them. Make the
rating and tag_string nullable so they don't have to be set when
creating uploads and can be ignored too.

db/migrate/20220203040648_drop_not_null_constraints_from_uploads.rb

@@ -0,0 +1,6 @@
+class DropNotNullConstraintsFromUploads < ActiveRecord::Migration[7.0]
+  def change
+    change_column_null(:uploads, :rating, true)
+    change_column_null(:uploads, :tag_string, true)
+  end
+end

db/structure.sql

@@ -1947,10 +1947,10 @@ CREATE TABLE public.uploads (
     source text,
     file_path character varying,
     content_type character varying,
-    rating character(1) NOT NULL,
+    rating character(1),
     uploader_id integer NOT NULL,
     uploader_ip_addr inet NOT NULL,
-    tag_string text NOT NULL,
+    tag_string text,
     status text DEFAULT 'pending'::text NOT NULL,
     backtrace text,
     post_id integer,
@@ -5775,6 +5775,7 @@ INSERT INTO "schema_migrations" (version) VALUES
 ('20220110171023'),
 ('20220110171024'),
 ('20220120233850'),
-('20220124195900');
+('20220124195900'),
+('20220203040648');