Extend the docs with tutorial 13

The tutorial 13 README could be converted into a tutorial in the NOMAD docs.

Specifically part 3 on plugin development: https://github.com/FAIRmat-NFDI/AreaA-Examples/tree/main/tutorial13/part3

and part 4 on deploying an Oasis with custom plugins: github.com/FAIRmat-NFDI/AreaA-Examples/tree/main/tutorial13/part4

Maybe we could also include part 2 and a bit on yaml schema writing in between.