fix(coderd): ensure that user API keys are deleted when a user is (#7270)

Fixes an issue where API tokens belonging to a deleted user were
not invalidated:
- Adds a trigger to delete rows from the api_key stable when the
  column deleted is set to true in the users table.
- Adds a trigger to the api_keys table to ensure that new rows
  may not be added where user_id corresponds to a deleted user.
- Adds a migration to delete all API keys from deleted users.
- Adds tests + dbfake implementation for the above.

coderd/database/migrations/000120_trigger_delete_user_apikey.down.sql

@@ -0,0 +1,9 @@
+BEGIN;
+
+DROP TRIGGER IF EXISTS trigger_update_users ON users;
+DROP FUNCTION IF EXISTS delete_deleted_user_api_keys;
+
+DROP TRIGGER IF EXISTS trigger_insert_apikeys ON api_keys;
+DROP FUNCTION IF EXISTS insert_apikey_fail_if_user_deleted;
+
+COMMIT;