Is there an existing issue for this?

• I have searched the existing issues

Feature description

I prefer not to use the real regions when doing tests or local stuff to make sure that if it accidentally picks up real credentials, it won't actually create or interact with resources in AWS. This used to work find in localstack - I even dug through the code to find that there is an option in the RegionStore to disable validation of the region string. At some point, you removed any way to disable that validation though, which means it just fails all requests using a custom region.

🧑‍💻 Implementation

There's already a flag that is passed to the account and region store constructors to disable validation. Seems like an environment variable or configuration flag to disable validation could be propagated.

Anything else?

No response