LLMs: Add strategy LLM

[Hialus]

Motivation

We want to ensure a high availability of Pyris. For this, a fail-over system would be helpful.

Description

This PR adds a strategy llm class for guidance. This class is able to switch between other LLM implementations dynamically. For this, it acts partially as a proxy to the other LLMs, while taking over certain areas to select the LLM to use before each call.
The strategy it uses is this:

1. Check which models support the currently required context length
2. Check which models are currently available
3. Select the first remaining LLM
   • If no LLM remains, take the one with the biggest context length
4. Execute the call with the LLM
5. If the call fails try again with the second LLM (if available)

This PR also adjusted some other parts of Pyris to support this new structure.