Support invocations_ws in agent init

[v1212]

Summary

• Adds invocations_ws as a selectable protocol for azd ai agent init.
• Keeps the no-prompt/default protocol as responses and documents invocations_ws in agent help/schema descriptions.
• Adds regression coverage for websocket protocol selection and code deploy serialization via protocol_versions.

Validation

• go test ./... from cli/azd/extensions/azure.ai.agents
• go build ./... from cli/azd/extensions/azure.ai.agents
• azd x build from cli/azd/extensions/azure.ai.agents

Live validation

• Local extension build installed successfully.
• azd ai agent init --protocol invocations_ws is accepted and reaches template selection, confirming protocol parsing no longer rejects it.
• Full azd deploy hello-world --no-prompt is currently blocked locally because the global azd auth cache is signed into JianWu@activityprotocol66.onmicrosoft.com, which cannot resolve the TTL subscription tenant. I did not run global azd auth login to avoid disrupting other local agent work.