Add multi year investment tutorial

[gnawin]

(description of changes)

Fixes #1041

Checklist before merging

• Documentation is up-to-date
• Unit tests have been added/updated accordingly
• Code has been formatted according to SpineOpt's style
• Unit tests pass

[tarskul]

There was a tutorial missing on capacity planning. That is now in the works (#1049). This tutorial should build on that. Both tutorials are perhaps even small enough to be combined into one.

[gnawin]

Thanks and good to know @tarskul. After checking #1049, I think we can merge these two because basically everything mentioned in that tutorial is already covered in this one and this one takes it even further by talking about details of milestone years. So I propose to close that one, and you can add to this PR if wanted.

[tarskul]

Ah, uhm, I already merged it to master. But don't worry, I'll combine them later. Is this branch based on master or an experimental branch? If it is based on master, I can merge master into add-multi-year-tutorial and then combine the tutorials.

[gnawin]

No worries. It is based on master (after your recent doc overhaul at least).

[gnawin]

@tarskul I added the missing figures. You may want to merge this after you align with the other tutorial.

Or maybe it is more convenient if we keep both for now, and do something later because they talk about slightly different topics, and I can soon expand this tutorial with more economic representations. If so, I'll just add a reference to the other tutorial and merge this.

[tarskul]

@gnawin In a local branch I'm trying to combine the two tutorials as they are both about capacity planning. I'll see how that goes. But if more tutorials are coming, we should perhaps list them in #735 such that we have an overview and can see what would fit where exactly. If there are indeed many things they could perhaps become an 'advanced' tutorial. We'll see.

[gnawin]

Cool! There will not be more tutorials from my side, but my plan is to populate this tutorial by adding more stuff about using economic parameters. I can start populate once this has been merged.

And I list the multi-year tutorial in #735 along side your capacity planning tutorial. That is a separate issue/tutorial because it is part of the multi-year investment epic #908

[tarskul]

This is what I have so far. I think it works as a tutorial. I'll just have to try the tutorial myself and see whether it also actually runs.

If that is ok with you, then we may ship it soon.

As for the other economic parameters, let's discuss them at some point to see whether it makes more sense to add them to this tutorial or to make a separate tutorial for them.

[gnawin]

Yes, if everything works, you can merge this.