Make some package installs in the devcontainer optional #70

Currently, the devcontainer installs all the packages that are configured. This approach leads to a bulkier container image, which then increases the time it takes to create a Codespace initially.

To potentially alleviate this, consider making some package installations optional. Instead of executing the installation scripts during the devcontainer's build process, we can keep these scripts available on the file system. This way, devcontainers that come later can choose to install only the packages they need.