Add httpx as runtime dependency for agentframework tooling extension

httpx is now used directly in mcp_tool_registration_service.py to create
AsyncClient instances with pre-configured headers. Without this explicit
dependency, consumers could hit ModuleNotFoundError if httpx isn't
available through transitive dependencies.

Author: JosinaJoy

libraries/microsoft-agents-a365-tooling-extensions-agentframework/pyproject.toml

@@ -28,6 +28,7 @@ dependencies = [
     "agent-framework-azure-ai >= 1.0.0b251114",
     "azure-identity >= 1.12.0",
     "typing-extensions >= 4.0.0",
+    "httpx >= 0.27.0",
 ]
 
 [project.urls]