DNS-2700: [webhook] add FOSSA workflow

[rizalgowandy]

This repo does not have automated dependency analysis or license compliance checks.

This creates risks in terms of:

• Missing critical vulnerabilities in dependencies.
• Potential usage of dependencies with incompatible or unapproved licenses.
• Lack of visibility into dependency changes over time.
• Enabling FOSSA ensures automated, continuous scanning of dependencies and license compliance across the codebase.

[Copilot]

Pull Request Overview

This PR introduces automated dependency analysis and license compliance checking by adding a FOSSA workflow to the GitHub Actions pipeline. The workflow helps mitigate security risks by scanning dependencies for vulnerabilities and ensuring license compliance.

Key changes:

• Addition of FOSSA workflow for continuous dependency and license scanning
• Configuration for multiple trigger events including push, pull requests, and merge groups

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