.Net: Option #2 - Refactor to support generic LLM request settings (use object)

[markwallace-microsoft]

Motivation and Context

Currently the SK core uses a model for LLM request settings which is OpenAI specific. This is a refactor to remove this assumption and to allow SK to be LLM agnostic.

Resolves: #2735

Description

1. Remove ChatRequestSettings and CompleteRequestSettings and use dynamic instead
2. Create default OpenAI request settings classes and code to create instance from an object. The object can be an instance of the expected request settings, a JsonElement or an anonymous type.
3. Fix up planner, unit tests and integration tests
4. Add a new Kernel syntax example showing all options to configure LLM request settings

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 😄

[markwallace-microsoft]

See: #2829