feat(contents): add signatures for commit and file content

Feature Request

1. User story

As an analyst,
I need to evaluate strings in commit headers, commit messages, and file content
In order to mitigate leakage risk.

2. Acceptance criteria

We'll be done when there is a Signature for:

• 1. AWS API Keys
• 2. Facebook OAuth
• 3. Generic API Keys
• 4. Generic Secrets
• 5. GitHub
• 6. Google (GCP) Service-accounts
• 7. Google OAuth
• 8. Heroku API Keys
• 9. PGP private key blocks
• 10. Passwords in URLs
• 11. RSA private keys
• 12. SSH (DSA) private keys
• 13. SSH (EC) private keys
• 14. SSH (OPENSSH) private keys
• 15. Slack Tokens
• 16. Slack Webhooks
• 17. Twilio API Keys
• 18. Twitter OAuth

3. Notes

⌦ Provide additional information here, if you need to.