Implement settings file for Ollama agent

[kborowinski]

PR Summary

This PR implements basic settings file for Ollama agent:

1. The settings file is stored at $HOME\.aish\agent-config\ollama\ollama.config.json
2. Currently only model and endpoint parameters are stored in the config file.

3. Default config file is created when none exists:

   {
   // To use Ollama API service:
   // 1. Install Ollama:
   //      winget install Ollama.Ollama
   // 2. Start Ollama API server:
   //      ollama serve
   // 3. Install Ollama model:
   //      ollama pull phi3
   
   // Declare Ollama model
   "Model": "phi3",
   // Declare Ollama endpoint
   "Endpoint": "http://localhost:11434"
   }

PR Context

This PR allows user to specify custom Ollama model and Ollama enpoint location, instead of hardcoded values. This partially implements #155 (no history and streaming)

@StevenBucher98 : This is quick and dirty, but I needed the settings file ASAP to test the different models without constant agent recompilation. I'm open for suggestions.