Bringing back the Burgers equation example

[asinghvi17]

There was an example of training a Fourier neural network on the Burgers equation in the previous repo, following a paper. The dataset link is now down but there's a Google Drive link with the same data files. Otherwise we might consider reproducing those scenarios ourselves somehow, or perhaps rehosting the files as a Github archive if that's possible.

cf. SciML/FluxNeuralOperators.jl#138

It could simply live as an example of reproducing the paper's results, or a test that that paper is still working as intended under this framework.

[avik-pal]

Added a deeponet example for Burgers atm