.Net: Fix: telemetry sample app repeated calls to the same registered function

[TaoChenOSU]

Motivation and Context

Previously inside the telemetry sample app, the code registers a prompt-based plugin to the kernel and then invokes the plugin directly via InvokeAsync(). This is actually against the pattern we recommend. The direct result of this is the models with function calling feature could potentially invoke the same function repeatedly.

This is related to: #6154, #6281

Description

Instead of registering the plugin to the kernel for later use, we create the plugin without registering it to the kernel, so that the model doesn't have the same function at its disposal when completing a response.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄