Add support for display_name in sessions

[dylan-apex]

When you make a POST request to /apps/{app_name}/users/{user}/sessions, there's no support for display_name with VertexAI. _create_session in adk_web_server.py doesn't pass display_name, even if it's included in the request body. The rest of the VertexAI session creation process accepts **kwargs, so we could also pass **kwargs in the signature

[klateefa]

@dylan-apex Thank you for reporting this. I understand the request is currently under review. Please keep me posted if anything else is needed. Thanks for your patience.

[wuliang229]

Hi @dylan-apex please see #4164 (comment). We will come back to this FR.

[dylan-apex]

@wuliang229 #3480

[wuliang229]

@dylan-apex I do see the PR, it has the problem of a breaking database schema.