[privatedns] Add python client name customization to avoid SDK breaking (#44438)

Preserve the existing Python SDK client name PrivateDnsManagementClient
via @@clientName python override to prevent a breaking change when the SDK is
regenerated from TypeSpec. Mirrors the existing javascript and java overrides.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: msyyc

specification/privatedns/resource-manager/Microsoft.Network/PrivateDns/client.tsp

@@ -5,6 +5,7 @@ using Microsoft.Network;
 
 @@clientName(Microsoft.Network, "PrivateDnsManagementClient", "javascript");
 @@clientName(Microsoft.Network, "PrivateDnsManagementClient", "java");
+@@clientName(Microsoft.Network, "PrivateDnsManagementClient", "python");
 
 // Add .NET SDK config
 #suppress "@azure-tools/typespec-client-generator-core/client-option" "Customize generated C# resource names for expanded Private DNS record-set resources."