More graceful web app behavior when the indexer storage is unavailable

When the indexer storage is unavailable, queries to it return an HTTP error code.

Frontend queries should catch those errors and handle them gracefully, silently logging errors in the background.

A hotfix for this issue was to make all service indexer storage queries return None immediately.

Migrated from T1060 (view on Phabricator)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information