[dagit] Add id to Asset
Summary: Give the Asset type an id field to avoid Apollo cache issues. Not sure this is the most ideal ID value here (e.g. AssetKey(['table_info'])), so let me know if I should change it.
Test Plan: Buildkite, load Dagit and sanity check global search behavior and Assets page behavior.
Reviewers: prha, sandyryza
Reviewed By: prha
Differential Revision: https://dagster.phacility.com/D7222