Add more detectors

[pixincreate]

1. Firebase API keys
2. Twilio API keys
3. SendGrid API keys
4. Mailgun API keys
5. DigitalOcean tokens
6. Heroku API keys
7. NPM tokens
8. Discord tokens
9. OpenAI API keys
10. LinkedIn secrets
11. Azure storage keys
12. MongoDB connection strings
13. Cloudinary URLs
14. Private key contents
15. DockerHub tokens
16. CircleCI tokens
17. Square access tokens and secrets
18. YouTube API keys
19. Google OAuth tokens

[pixincreate]

closed with #4