Refactor Docker setup and CI workflows for improved build process

[marc-hanheide]

This pull request refactors the devcontainer setup for the robotics teaching platform, modernizing the Docker build process, simplifying configuration, and updating CI workflows. The main changes include switching to a new base image, restructuring the Dockerfile for improved dependency management and build efficiency, updating devcontainer configuration files, and introducing new GitHub Actions workflows for building and testing containers. Legacy files and configurations have been removed to streamline the setup.

Container and Build System Modernization

• The .devcontainer/Dockerfile now uses lcas.lincoln.ac.uk/lcas/limo_platform:2 as the base image, restructures build stages for better dependency management, and improves cleaning and build steps for efficiency.
• The devcontainer configuration is updated in .devcontainer/devcontainer.json (renamed from a subdirectory), now referencing the new Dockerfile and build arguments for the updated base image.

CI/CD Workflow Updates

• A new GitHub Actions workflow .github/workflows/container-build,yml is added to automate multi-architecture Docker image builds and pushes to the LCAS registry. (.github/workflows/container-build,ymlR1-R68)
• The devcontainer CI workflow .github/workflows/dev-container.yml is revised to use the new build infrastructure, removing matrix builds and updating build steps for compatibility with the new container setup.
• The legacy ROS CI workflow .github/workflows/ros-ci.yml is removed, consolidating CI processes in the new workflows.

Configuration and Usability Improvements

• The post-create script .devcontainer/post-create.sh now robustly adds environment setup and useful aliases to .bashrc, sources both ROS and workspace environments, builds the workspace, and customizes the desktop background for students.

Cleanup of Legacy Files

• The obsolete .devcontainer/lcas.repos file, previously used for source repository configuration, is deleted as the new build process no longer requires it.