[OpcuaClient] Default ClientSignatureAlgorithm reference to AsymmetricSignatureURI

Similar to https://github.com/FreeOpcUa/python-opcua/pull/945
Small test: https://pastebin.com/SxUSnFi0

asyncua/client/client.py

@@ -407,7 +407,9 @@ class Client:
         if self.security_policy.AsymmetricSignatureURI:
             params.ClientSignature.Algorithm = self.security_policy.AsymmetricSignatureURI
         else:
-            params.ClientSignature.Algorithm = "http://www.w3.org/2000/09/xmldsig#rsa-sha1"
+            params.ClientSignature.Algorithm = (
+                security_policies.SecurityPolicyBasic256.AsymmetricSignatureURI
+            )
         params.ClientSignature.Signature = self.security_policy.asymmetric_cryptography.signature(challenge)
         params.LocaleIds.append("en")
         if not username and not certificate: