python: allow using allowed_errors.py (#7719)

See #7718. Fix it by renaming all `types.py` to `common_types.py`.

Additionally, add an advert for using `allowed_errors.py` to test any
added regex.

test_runner/regress/test_readonly_node.py

@@ -1,8 +1,8 @@
 import pytest
+from fixtures.common_types import Lsn
 from fixtures.log_helper import log
 from fixtures.neon_fixtures import NeonEnv
 from fixtures.pageserver.utils import wait_for_last_record_lsn
-from fixtures.types import Lsn
 from fixtures.utils import query_scalar