- Add storing bot response messages in postgres

- Add scheduled task to clean up said store

PluralKit.Core/Database/Migrations/11.sql

@@ -0,0 +1,17 @@
+-- SCHEMA VERSION 11: (insert date) --
+-- Create command message table --
+
+create table command_message
+(
+	message_id bigint primary key,
+	invoker_id bigint not null,
+	timestamp timestamp not null default now()
+);
+
+create function cleanup_command_message() returns void as $$
+begin
+    delete from command_message where timestamp < now() - interval '1 minute';
+end;
+$$ language plpgsql;
+
+update info set schema_version = 11;