getEncryptionPublicKey method
get it from atChops if we have it, otherwise try the keystore
Implementation
Future<String?> getEncryptionPublicKey(String atSign) async {
atSign = AtUtils.fixAtSign(atSign);
String? v = atChopsKeys?.atEncryptionKeyPair?.atPublicKey.publicKey;
v ??= (await keyStore!.get('${AtConstants.atEncryptionPublicKey}$atSign'))
?.data;
return v;
}