Experiment with reusable content

[eemilhaa]

Context: #79

This adds reusable lukuohje.Rmd & uses it for GP001 as an example.

In general, bringing in rmarkdown from other files works, but images seem to be an issue. If we keep the shared images in a centralized location (i.e. outside the course directory that gets built with bookdown) the images are not included in the build. A possible way to overcome this would be to copy images over as part of the build, but that of course adds more complexity.

[github-actions]

Preview changes here.

[JuhoErvasti]

@eemilhaa I'm on vacation so I'll get back reviewing this in August, but I happened to notice the GH notification so I'll just add in regards to the images is that one concern we've had with them is that they are the main thing that make this repo pretty big in disk size (which we've tried to minimize since GitHub does have some limits on repo sizes) and I think a solution which doesn't involve copying images would be preferred if possible.

One idea I remember having at some point is that maybe instead of copying we would somehow use direct links to the raw image content in the repo itself, something like https://raw.githubusercontent.com/GispoCoding/master-training-data/refs/heads/main/src/GR002/img/harjoitus_1/image1.png. And to keep things simpler from an editing point-of-view these would be replaced automatically (with a Python? script in the render-deploy workflow) so you could keep using the relative paths as is and render the documents locally but then there wouldn't be any duplication of images over to the pages branch. And I think then you could account for the shared images in the script.

But that's just an idea, do you think that would be a good/reliable approach? I guess it also adds its own complexity.

Anyway, I'll try to not look at this anymore until August, just wanted to quickly share the idea and to mention the repo size aspect.

[JuhoErvasti]

@eemilhaa I think the PR itself looks good and this approach is a good idea. The image links are the only issue, I think. What do you think of the idea in my previous comment and how should we continue with this?