Add CI leg for running A2A TCK tests

[adamsitnik]

Currently, we run the tests manually using the instructions provided here. I broke them at least once, I saw others do it to (by accident).

As suggested by @Blackhex, it would be great to automate this process.

[Blackhex]

Created Blackhex#1 for now as a proof-of-concept of the idea. The https://github.com/a2aproject/a2a-tck is undergoing massive refactor at the moment and its worth to wait and reconsider things after it will be done. Meanwhile, any feedback is welcome.

[brandonh-msft]

which tck sets would we want to have as part of this automatic check??

[Blackhex]

which tck sets would we want to have as part of this automatic check??

That's up to discussion and observation how mature they are/will be. For now, we can start with "mandatory" group.

On the other hand, from my personal perspective, the aspiration of this ticket is not necessarily to add a fully automated check but to easily allow to run it on demand via triggering the workflow manually or via GitHub bot.

[SamMonoRT]

Moving the tracking item to Not Ready for the .NET Intelligent App Project tracking purposes till we get someone assigned to this.

cc @karelz @aalina23