refactor: clean-up dockerfile

[steveiliop56]

This pull-request organizes and cleans up the Dockerfile for better readability and maintainability. The following changes were made:

• Remove use of the alpine image since it was only used to copy the source code
• Use tagged composer and php versions to avoid breaking distro or software updates
• Remove unnecessary packages like curl and vim-tiny
• Organize the Dockerfile in a source code, dependencies, config, runtime model improving readability
• Create volumes for the config, courses and video directories ensuring configuration persistence even if the end-user forgets to assign a named volume

Ideally the Debian based PHP image should be replaced with 8.3-alpine3.21 which would offer a far more lightweight image but I decided against it for now to avoid breaking any current setups that rely on Debian. Let me know if you need anything changed.