Replace terminal blocks with code blocks

[NucciTheBoss]

The v1 release of the Sphinx terminal plugin fixes our issue with being unable to multiline longer commands, however, the issue we now have is that we cannot have multiple commands in the same terminal block. This new behavior causes UX issues on how-tos like the Use Apptainer how-to where multiple commands are executed in an example:

The white border around the terminal blocks is quite visually distracting. Because of this UX issue, we should switch back to using shell code blocks for the majority of commands, and then only use the terminal block when we want to show example output to the reader to let them know that they're moving in the right direction.