New notebook with more details and simplistic example of using the Scheduler for bulk processing

[skarppinen]

Hello.

This PR suggests new documentation in the form of a Jupyter Notebook "06_transformations_and_the_scheduler.ipynb" which attempts to explain a bit about the inner workings of the Scheduler, and in particular, how the Scheduler passes data to the transformations. I believe there might be also other data-passing mechanisms that possibly could be covered here as well. This notebook grew out of my own misunderstandings of how Loki processes large source trees, so I believe it may be useful for other new users as well.

There are some blanks and probably even wrong information here that needs to be sorted out. In some bits I purposefully left things out because I was not sure what is the intended usage.

[FussyDuck]

All committers have signed the CLA.

[reuterbal]

Thanks Santeri, just to acknowledge that we've seen this and are keen to integrate it but it might take a little while to get around to it. Sorry about that!

[codecov]

Codecov Report

Merging #171 (a7ce67b) into main (03324ef) will not change coverage.
Report is 13 commits behind head on main.
The diff coverage is n/a.

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  Coverage   92.13%   92.13%           
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  Files          90       90           
  Lines       16689    16689           
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  Hits        15377    15377           
  Misses       1312     1312           

Flag	Coverage Δ
lint_rules	96.22% <ø> (ø)
loki	92.10% <ø> (ø)
transformations	91.40% <ø> (ø)

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