Authelia's metrics were scraped over loopback, declared only on a host
running both authelia and the collector, so a split deploy collected none.
Its target is now declared on every host as
`https://<swarm.authelia.domain>/metrics`, next to forgejo's, and authelia's
vhost serves `= /metrics` behind the same collector auth subrequest as the
forge's. The loopback entry is gone, so a single host still scrapes
authelia once, now by name.
The forge-only `metricsRule` becomes `metricsRules`, derived from every
`publishedScrapeTargets` entry. Each target gets the collector-scoped
`one_factor` rule followed by an unconditional `deny`. The `deny` is
needed because authelia 4.39 skips a rule whose `subject` does not
match and moves on. With nothing after the collector rule, any other
authenticated session reached `default_policy = one_factor` and was
admitted. That was already true of the forge's `/metrics`, and this
change closes it there too.
Part of #5205
393e84afd0