Send schema cache to Sentry on MissingAttributeError
We sometimes get this error on GitLab.com: https://gitlab.com/gitlab-org/gitlab-ce/issues/57727
We don't know what causes it. This change adds more information to the Sentry exception to try to pinpoint the issue.
Example Sentry issues: my dev environment, an Omnibus install. I generated the errors here by running this in a Postgres console after the application booted:
ALTER TABLE users RENAME COLUMN encrypted_password TO encrypted_password_2;