newAtKey method
Implementation
AtKey newAtKey(int ttr, String key, String? sharedWith, {int? ttl}) {
var atKey = AtKey()
..metadata = Metadata()
..metadata!.ttr = ttr
..metadata!.ccd = true
..key = key
..sharedWith = sharedWith
..sharedBy = atClient!.currentAtSign;
if (ttl != null) atKey.metadata!.ttl = ttl;
return atKey;
}