Feat: improve CI and docker builds

[nimish-ks]

🔍 Overview

This PR introduces the following changes and performance improvements to the GitHub Actions pipeline.

• Dedicated staging builds when a PR is opened to phasehq/backend-staging and phasehq/frontend-staging
• Parallel builds - backend and frontend docker builds happen in parallel and not sequential
• The staging build are only build for arm64 and doesn't require QEMU virtualization via dockerx speeding up the build time significantly
• Only PRs merged to main or the creation of a new release will trigger a build to deploy production images to phasehq/backend and phasehq/frontend
• Bump GitHub actions workflows dependencies