Add a Durable Functions app for OpenAI Agent samples and an orchestrator for the basic/hello_world sample

[AnatoliB]

This PR converts the openai_agents/basic/hello_world.py sample into a Durable orchestrator.

You can invoke it like this:

$r = irm 'http://localhost:7071/api/orchestrators/basic_hello_world_orchestrator'
irm $r.statusQueryGetUri

Example output:

name            : basic_hello_world_orchestrator
instanceId      : 0bb5ea28e72f414babc48a4fb544827d
runtimeStatus   : Completed
input           : 
customStatus    : 
output          : Code calls itself back,  
                  A loop within a function,  
                  Infinite mirrors.
createdTime     : 8/4/2025 6:16:44 AM
lastUpdatedTime : 8/4/2025 6:16:49 AM

This is not a demonstration of the intended final result. This PR wraps the entire agent invocation into an explicitly defined activity. This is done just so that this app builds and runs. Instead of wrapping this code in an activity function like this, we should be able to invoke it from the orchestrator directly. In order to enable this, Runner.run invocations should be implicitly wrapped in activity invocations, and this is what we should do next.

[nytian]

Can we include the PR description as a README.md file in this sample directory? That would be more clear and also helpful for customer who uses this sample.