Whether a site answers, from here -- what its users see: the status, the time, the text the application alone writes, and how long its certificate has left.
class MMO\admin\monitoring\probes\HttpProbe extends MMO\admin\monitoring\aProbe
It asks what the deployment's health check asks: the target's `url` with its `healthPath`, expecting its
`healthExpect` (deploy.json), so a site is judged the same way the release that put it there was. `{checksum}` in an
expected text (a release's own stamp) is dropped: the hub does not know which release should answer.
A site that does not answer, answers an error or lacks the expected text is critical, whatever the thresholds say.
Metrics: `http.code`, `http.timeMs`, `http.ttfbMs`, `http.sizeKb`, `tls.daysLeft`. Facts: `url`, `ip`, `server`,
`certificate`, `issuer`.