ADK Session should have display_name and align with AgentEngine Sessions interface

[ashubham]

Is your feature request related to a problem? Please describe.
VertexAI AgentEngine Sessions supports properties which help in naming the session displayName and filtering labels. These are not present in ADK, making it hard to filter/name the session.

DisplayName is very basic as it serves like the title of the session, otherwise the user sees a list of ids in the list. Which is not friendly at all.

These are the ones present in ADK:
https://github.com/google/adk-python/blob/main/src/google/adk/sessions/session.py

  id: str
  """The unique identifier of the session."""
  app_name: str
  """The name of the app."""
  user_id: str
  """The id of the user."""
  state: dict[str, Any] = Field(default_factory=dict)
  """The state of the session."""
  events: list[Event] = Field(default_factory=list)
  """The events of the session, e.g. user input, model response, function
  call/response, etc."""
  last_update_time: float = 0.0
  """The last update time of the session."""

Look at this for the complete structure:

https://docs.cloud.google.com/vertex-ai/generative-ai/docs/reference/rest/v1/projects.locations.reasoningEngines.sessions#Session

Describe the solution you'd like
The ADK Session object should support display_name and labels as additional optional properties.

Describe alternatives you've considered
Patching the ADK classes with additional fields, but it seems might break in certain places. Also, will not be validated/serialized by Pydantic.