Add config file support and structure for multiple LLMs

[MikeGarde]

Migrations

• Adjusted the version specification of serde for consistency and clarity.
• Enhanced release profile settings for optimization.

Dependencies

• Introduced the dirs and toml crates to facilitate reading from configuration files.
• Added development dependencies (assert_cmd and predicates) to aid in testing and command assertions.

README

• Updated the README.md to detail reading from a configuration file and future multi-LLM support.
• Added a privacy notice for OpenAI processing only.
• Included a new "Prove It!" section for practical usage demonstration.
• Clarified installation prerequisites regarding the OpenAI API key.

Models

src/config.rs

• Introduced a Config struct consolidating configuration settings for model selection.
• Implemented from_sources method to read configurations from multiple sources (CLI, env vars, TOML, defaults).
• Created utility functions to find and read a TOML configuration file, enhancing user customization.
• Established groundwork for supporting multiple models in the future.

src/llm/mod.rs

• Introduced LlmClient trait for a standardized LLM interface.
• Implemented NoopClient struct for testing purposes without a functional LLM.
• Prepared code structure for future LLM integration.

src/llm/ollama.rs

• Introduced ollama.rs for future functionality related to a specific LLM.
• Organized code structure to lay the groundwork for multiple LLM support.

src/llm/openai.rs

• Introduced LlmClient implementation for OpenAI, enabling requests to the OpenAI Chat Completions API.
• Implemented methods for summarizing files and generating commit/PR messages.
• Added data structures for managing API requests/responses.

Main Application

src/main.rs

• Introduced config and llm modules for better organization and future multi-LLM support.
• Changed struct fields and methods to public for external access.
• Updated configuration resolution to use the new Config module.

Tests

tests/cli_basics.rs

• Added cli_basics.rs to validate CLI behavior, ensuring correct responses to --help and --version flags.
• This supports the ability to read from a config file while ensuring proper CLI interaction.