[ rust-nostr/nostr ] gossip: add `GossipAllowedRelays` to filter relays during selection

Closes nostr:nevent1qvzqqqqx25pzpepndn2jthmelfxn4umylktqp493ph8yy9d2fse76al2ppprgjcsqqsxjcxdfc5vt8hhqfqfgcynk32ls3fgduxzx4xlevldceuj4sk9kvsgx4h5j

Pull-Request: https://github.com/rust-nostr/nostr/pull/1128

Signed-off-by: Yuki Kishimoto

https://github.com/rust-nostr/nostr/commit/a0b8dc139a8de15b726ec2648f6597afd9c7e795