Dem variable cell weight for load balancing

[OGaboriault]

Description

When load balancing, the base weight of every cell was set at 1000. This feature allows the cell weight to vary depending on its barycenter position by using a parsed function. This way, the cell weight could vary over space an time.

This will be useful when dealing with static dem problem, where you can only load balance once at the start on the simulation to keep track of the tangential overlap. Cells where we know the particle are going to be could be assign a bigger weight then those where no particle will be present.

This PR is in WIP for now. I just want to see if the test are failling in dealii 9.6 on the CI .

Testing

Test need to be implemented.

Documentation

cell weight function is a dim function outputing a scalar value. This function will be evaluated at every load balancer for every cell barycenter.

Checklist (will be removed when merged)

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