Add uksouth hosted agent region (#8964)

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

Author: 3 people

cli/azd/extensions/azure.ai.agents/internal/cmd/hosted-agent-regions.json

@@ -18,6 +18,7 @@
         "spaincentral",
         "swedencentral",
         "switzerlandnorth",
+        "uksouth",
         "westus",
         "westus3"
     ]