Support for reloading agents on file change

[Babsvik]

Is your feature request related to a problem? Please describe.
Reloading agent files when they change, like --reload_agents in https://github.com/google/adk-python . This is also described as a wanted feature in google/adk-docs#102 and was implemented in google/adk-python@e545e5a

Describe the solution you'd like
Watch agent files and reload when they change, possibly using https://github.com/paulmillr/chokidar.

Describe alternatives you've considered
N/A

Additional context
I will try to write up a PR when I get a chance, if anyone gets to it before me - Great!

[Varun-S10]

Hi @Babsvik, Appreciate the suggestion and your willingness to contribute. I will escalate this feature request to the team.

Hi @kalenkevich, Could you please review this feature request ?

[ScottMansfield]

What kinds of behavior changes do you expect to see when a file is saved?

IMO we should reload the agents but only use the new one for newly created sessions, leaving the old definition attached to existing sessions. I can see an argument for changing the agent definition of existing sessions, but I think that will create a lot of problems with consistency. We could consider some way to differentiate the reloaded versions and expose that to the user, but I don't know how.