add dnslink namespace

Rationale:
- been around since  the very early days, seems we just never added it?
- we already have dnsaddr, which works similar way, but for multiaddrs  (TXT records)
- we want to support IPNS-agnostic recursive TXT values `dnslink=/dnslink/example.com`
- we need a way for pinning DNSLink names within Pinning Service API

table.csv

@@ -34,6 +34,7 @@ dns,                            multiaddr,      0x35,           permanent,
 dns4,                           multiaddr,      0x36,           permanent,
 dns6,                           multiaddr,      0x37,           permanent,
 dnsaddr,                        multiaddr,      0x38,           permanent,
+dnslink,                        namespace,      0x39,           permanent,
 protobuf,                       serialization,  0x50,           draft,     Protocol Buffers
 cbor,                           ipld,           0x51,           permanent, CBOR
 raw,                            ipld,           0x55,           permanent, raw binary