enable dependabot

[ljubon]

Enable DependaBot security feature Useful links:

• https://docs.github.com/en/code-security/supply-chain-security/managing-vulnerabilities-in-your-projects-dependencies/about-alerts-for-vulnerable-dependencies
• https://docs.github.com/en/code-security/supply-chain-security/managing-vulnerabilities-in-your-projects-dependencies/about-managing-vulnerable-dependencies#dependabot-alerts