Add automated thank you comment on merged PRs

[xkaper001]

Description

Add a GitHub Action workflow to automatically post a cool and encouraging thank you comment when a PR gets merged.

Motivation

To appreciate and encourage contributors when their PRs are successfully merged into the project.

Implementation Details

• Create a new GitHub Actions workflow that triggers on PR merge events
• Post an automated, friendly thank you message to merged PRs
• Message should be encouraging and show appreciation for the contribution

Acceptance Criteria

• Workflow triggers only on merged PRs
• Comment is posted automatically
• Message is friendly and encouraging
• No comments on closed (but not merged) PRs

[github-actions]

👋 Thanks for opening this issue and contributing!

Our reviewers will check it soon 🚀

📘 If you’d like to know more about contributing, please read our CONTRIBUTING.md.