Unclear error messages from 403 when Grafana quotas hit

[stevesg]

Noticed in alerting but may affect other resources (unknown)

Grafana canonically returns 403 when quotas are hit, but the body of the response is not read and displayed to the user. This means when e.g. they hit their alert rules quota, they see what looks like auth/permissions errors, instead of the quota message that Grafana returns.