Add DFT-FE publications

[bangerth]

The DFT-FE code is based on deal.II. I think it would be fair game to add all of the publications based on that code to our list as well. Their list is here: https://sites.google.com/umich.edu/dftfe/publications?authuser=0 Their foundational publications are listed here, and we should add those as well: https://sites.google.com/umich.edu/dftfe/referencing?authuser=0

[bangerth]

#622 deals with the "foundational publications" and then collects everything from the bottom up to the following entry:

Shojaei, M.F., Holber, J., Das, S., Teichert, G.H., Mueller, T., Hung, L., Gavini, V., Garikipati, K., 
Bridging scales with machine learning: From first principles statistical mechanics to continuum phase field computations to study order-disorder transitions in LixCoO2, 
Journal of the Mechanics and Physics of Solids 190, 105726 (2024).

Let's just keep this PR open so we can periodically update what's new on their page.