Add auto_delete_at to environments

Adds a new column for storing a timestamp after which the environment
is allowed to be auto-deleted.

db/migrate/20210128114526_add_auto_delete_at_to_environments.rb

+# frozen_string_literal: true
+
+class AddAutoDeleteAtToEnvironments < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  def up
+    with_lock_retries do
+      add_column :environments, :auto_delete_at, :datetime_with_timezone
+    end
+  end
+
+  def down
+    with_lock_retries do
+      remove_column :environments, :auto_delete_at
+    end
+  end
+end

db/schema_migrations/20210128114526

+ad83205a0203427ccad1c25933e28cf13ebfb0274865ce5f0f2d578e84bb07a3
\ No newline at end of file

db/structure.sql

@@ -12105,7 +12105,8 @@ CREATE TABLE environments (
     environment_type character varying,
     state character varying DEFAULT 'available'::character varying NOT NULL,
     slug character varying NOT NULL,
-    auto_stop_at timestamp with time zone
+    auto_stop_at timestamp with time zone,
+    auto_delete_at timestamp with time zone
 );
 
 CREATE SEQUENCE environments_id_seq