feat: support multiple relays

[rolznz]

PR can be tested with Alby JS SDK: getAlby/js-sdk#486

TODOs

• implement commented out code / FIXMEs (e.g. publishing after app deletion)
• thorough testing
  • automatic reconnection (our reconnection code was removed) - this is handled by the pool, re-connections after 3+ seconds (there is backoff logic)
  • If the hub starts subscribing when the relay is down, will it reconnect to the relay once the relay comes back up? Yes (+ republishes info events for that relay)
  • check duplicate event handling on hub side when JS SDK publishes request to both relays - Logs "Event already processed" warning - not an issue (other reaons for this e.g. client for some reason publishes an event twice) - NOTE: this is an issue in go-nostr - Fernando to submit a PR to properly de-duplicate events
  • what happens if new app is created when one relay is down then the other relay goes down and the first relay is up again? publish retries are now on a per-relay level
  • what happens to notifications sent to one online relay, then another relay comes back online (notification was successful for first relay, nothing needed to do)
  • app is created when all relays are down and then relay is reconnected - does it publish info event? yes
  • Ensure clients that don't support multiple relays still work as before (and pick the first relay from the list)
    • Alby JS SDK (pre-multi relay support)
    • Primal iOS - zaps work
    • Damus - wallet displaying balance works
    • Amethyst - only takes first relay param when configuring URL, zaps work
    • https://supertestnet.github.io/nwc_tester/ - no - takes the last relay because of its custom NWC URL handling code rather than using standard url parsing
  • test nwc_app_updated when relays online
  • test app deleted (should remove info event from relay)
  • ensure nwc_app_updated later publishes when offline relay comes back online
• Display relays in UI a bit better (Show online status?)
• Add second Alby relay to default config (currently only has one relay) - moved to Add second relay to default config #1887 - will be deployed in a separate hub version
• what happens if we fail to publish the info event to one relay? (hub would have to restart to later publish to it)
• Test 1-click flow (HTTP version)
• Test 1-click flow (NWA version)

Notes:

• Spec changes

  • 1-click connection flow has relayUrl for http callback. This is wrong, probably best to call it relayUrls and keep relayUrl for backward compatibility until apps update (e.g. bitcoin connect) - added comment on existing client created secret PR.
  • clarify nip-47 spec for multiple relays (relay=firstrelay&relay=secondrelay) - should not needed - standard way to pass the same property multiple times in a URL)

  Move to new issue:

  • Consider updating to use fiatjaf's new library https://gitworkshop.dev/npub180cvv07tjdrrgpa0j7j7tmnyl2yr6yr7l8j4s3evf6u64th6gkwsyjh6w6/relay.ngit.dev/nostrlib (or move to a new issue)