Add automated welcome workflow for first-time contributors

### 🔖 Enhancement description This enhancement proposes adding a GitHub Actions workflow that automatically posts a welcoming comment when a user opens their first Issue or Pull Request. ### 🎤 Pitch Open-source projects thrive on community engagement, but manually greeting every first-time contributor can be time-consuming for maintainers. Implementing this automated welcome workflow would benefit the Appwrite repository by: * **Improving the onboarding experience:** It provides immediate, warm feedback to users who are taking the time to report bugs or write code for the first time. * **Guiding newcomers:** By linking directly to `CONTRIBUTING.md` right away, we ensure new contributors read the guidelines *before* maintainers need to step in and review. * **Saving maintainer time:** It automates the routine task of sharing boilerplate onboarding links, allowing the team to focus strictly on triaging the issue or reviewing the code. ### 👀 Have you spent some time to check if this issue has been raised before? - [x] I checked and didn't find similar issue ### 🏢 Have you read the Code of Conduct? - [x] I have read the [Code of Conduct](https://github.com/appwrite/.github/blob/main/CODE_OF_CONDUCT.md)