Made it possible to choose ElevenLabs voice via a Command Line Argument

[th8m0z]

• Changed the default male and female voices from "Paola" and "Arthur" to "Rachel" and "Adam" to avoid errors where the previous ones might not be part of the voice collection for all users
• Added a command line argument --voice so users can pick which ElevenLabs voice they want to use for the voiceover. Example: python3 run.py --voice "Callum"
• Fallback to default voices in case that user specified voice does not exist

Let me know if this works for you, happy to make changes if you'd like other default voices for example.