Add start button

[ishaan1013]

Similar to replit's start button.

Note: there's already a start button for this in the sidebar/index.tsx file which is commented out, we should probably just uncomment this and implement the logic

• should be configured by default to the project type (react: npm i && npm run dev)
• should be configurable (modal to change default terminal commands)
• the button will create a new terminal and run the configured commands