Python A2a integration

[Shubham-Kumar-2000]

Hi,

From the past few months I am using a custom code for a2a integration.
I raised the PR for this around 5 months ago, but then we didn't had sessions and history providers thus it was kept on hold but few months back even that was fixed.

It would be great if I could get some attention on the PR such that I could get rid of the duplicate code on my repo and use it inbuilt.

Do let me know if something needs update from my end.

Thanks in advance. cc @eavanvalkenburg @markwallace-microsoft