add GitHub Actions CI/CD pipeline

[AldrionDev]

Summary

Added a GitHub Actions CI/CD pipeline for the Dockerized HTTP server.

Changes

• Runs Go tests on pull requests and pushes to main
• Builds the Docker image
• Publishes the Docker image to GitHub Container Registry on pushes to main
• Tags the image with latest and commit SHA
• Documents required workflow permissions

Test

go test ./...
docker build -t http-server-devops:local .