.Net: Examples with FrugalGPT techniques for LLM cost and performance improvements

[dmytrostruk]

Motivation and Context

This PR shows how to use FrugalGPT techniques to reduce cost and improve LLM-related task performance with Semantic Kernel filters.
More information about FrugalGPT: https://arxiv.org/abs/2305.05176

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 😄