Add user customization options

[Madhuvod]

This PR adds the ability for users to customize voice settings in the VoxLingua application.

Changes Made:

• Enhanced text_to_speech module to accept pitch and speed parameters
• Added voice customization sliders to the UI
• Expanded language options for better user experience

This addresses one of the future improvements mentioned in the README: "Enable additional customization options for the user."

Technical Details:

• Added pitch and speed parameters to the text_to_speech function
• Implemented ffmpeg-based voice modification for pitch and speed adjustment
• Updated the Gradio interface to include sliders for these parameters