Added changes mentioned in issue: #305

[ArifShariar]

I have added changes mentioned in the issue #305

1. Multiple output formats: JSON, SRT and TXT. Users can select the output format from menu
2. Users can choose the whisper model.

Fixed bug:

1. If the output directory already exists, it throws an error. Added a check for that so that it does not create a new directory if one already exists.
2. Comparison using "is" is replaced with "=="

[github-actions]

Greetings! This is an automated message from GitHub Actions. 🤖
Your pull request has been received and is awaiting for a review by the repository owner or a maintainer. This may take some time, so please be patient.
While you wait, you can continue to work on other issues or pull requests, or explore the project further. Or you can simply relax and enjoy your day.
Thank you for your contribution to this project! You are awesome! ⭐

[Mrinank-Bhowmick]

Hey @ArifShariar
Thanks for the changes 🚀
Happy Hacktoberfest ⭐