added chars and test for asset key validation. fixed errors thrown in validate_asset_key_string and validate_structured_asset_key, as they were not thrown correctly and would error out if reached.
Summary: Fixes https://github.com/dagster-io/dagster/issues/2965. Also fixes faulty error throws in asset key validation methods.
Test Plan: Added new tests to ensure functionality
Reviewers: sandyryza, yuhan
Reviewed By: sandyryza
Differential Revision: https://dagster.phacility.com/D4577