feat(webnsupdate): add handling for multiple IPs

Specifically, for when both and IPv6 and and IPv4 addr is provided. This
ensures we can forward both addrs to webnsupdate, instead of only
allowing IPv4.

Cargo.toml

@@ -27,6 +27,8 @@ clap-verbosity-flag = { version = "3", default-features = false, features = [
 http = "1"
 miette = { version = "7", features = ["fancy"] }
 ring = { version = "0.17", features = ["std"] }
+serde = { version = "1.0.217", features = ["derive"] }
+serde_json = "1.0.137"
 tokio = { version = "1", features = ["macros", "rt", "process", "io-util"] }
 tower-http = { version = "0.6.2", features = ["validate-request"] }
 tracing = "0.1"