Review feedback: the metrics pair had nothing writing into it, and it sat
outside the switch that turns on every other swarm-wide service.
The collector now exports to VictoriaMetrics as well as upstream — a
fan-out, not a choice: a local store is for looking at this swarm, an
upstream is for whoever aggregates across swarms.
That makes a local store a complete destination on its own, so
`otel.endpoint` is no longer required when it runs here; a hive with
neither is still refused. The assertion only ever relaxes, so every
config that evaluated before still does.
`enableRequiredServices` now derives both halves, alongside matrix,
authelia and nats. They derive together because a store with no UI is
unreadable and a UI with no store is empty.
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