Add working Julia environment(s) for the examples (toml files)

[carstenbauer]

Currently, one can't run the examples without manually adding the necessary packages (e.g. ImplicitGlobalGrid or MPI). Would be great to have toml files in examples/ that make it a simple ] instantiate.

[omlins]

Thanks for the suggestion @carstenbauer! That's a good point for possible improvement. However, I am not sure how it should look like as in the same time, we would not like to scare off, e.g., newcomers with multi-file examples. Personally, I am very much a fan of single-file examples and the examples should work with, a priori, any recent enough combination of packages - was this not the case for you?

In brief, I am not sure what we should do; one option might be to create toml files shared by all examples.

[luraess]

one option might be to create toml files shared by all examples.

I would suggest this option. one caveat being that some examples not relying on IGG may still have that part instantiated.