Use auth_rate_limit_ip() rather than $request->ip() for the api, 5 and
feedback rate limiters. On cloud, each client behind Cloudflare now gets
its own bucket instead of sharing the proxy's bucket. Self-hosted
instances ignore the CF-Connecting-IP header.
Add feature tests for per-client sentinel push buckets on cloud and for
ignoring the header on self-hosted.
Add scripts/restore-backup-vm.sh, which restores an instance backup into
an offline KVM VM to test database migrations. Bump the v4 version in
other/nightly/versions.json to sha-1e9add3.