Pin VS Code version

[tibynx]

This pull request updates Docker image build process and GitHub Actions workflow to improve how the VS Code package version is handled and tagged.

Workflow and build improvements:

• The GitHub Actions workflow (.github/workflows/build-image.yml) now extracts both the full package version and a simplified image tag, making image tags cleaner and more predictable.
• The workflow passes the simplified image tag to Docker, and updates all image tags and labels to use this new value, ensuring consistency across GitHub Container Registry and Docker Hub.
• Changed the naming of some steps.

Dockerfile improvements:

• The Dockerfile now accepts an INSTALL_VERSION build argument, allowing it to install the exact VS Code version determined in the workflow, which improves reproducibility and transparency.