chore: add agentic first-time contributor workflow

[Junnygram]

Description

This PR replaces the legacy (or missing) newcomer welcoming logic with a modern, agentic workflow using the gh-aw framework. This is part of the effort to standardize and harden newcomer onboarding across the Meshery ecosystem.

Key Features:

• Personalized Onboarding: The assistant analyzes the PR content and provides tailored resource links based on the specific files touched (e.g., schemas vs. documentation).
• Hardened Bot Filter: Includes a production-grade filter to ignore Dependabot, Copilot, and other automated agents, reducing notification noise.
• DCO Compliance: Automatically checks for commit sign-offs and provides immediate fix instructions if they are missing.
• Security: Hardened with checkout: false to prevent untrusted code execution during the pull_request_target event.

Next Steps

This workflow is being evaluated for its effectiveness in providing high-quality, relevant guidance to first-time contributors.

[github-actions]

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[Bhumikagarggg]

@Junnygram Thank you for your contribution! Let's discuss this during the website call tomorrow at 5:30 PM IST | 7 AM CST Add it as an agenda item to the meeting minutes, if you would 🙂

[KatalKavya96]

Hi @Junnygram, thanks for working on this.

Could you please link the native issue URL that this PR is addressing?

Also, are there any updates on this workflow since it was planned to be discussed in the website call? Would be helpful to know the current status or next steps for this PR.