Draft: Feature/hybrid cvfe

What this MR does / why does DuMux need it:

Implementation of hybrid pq1bubble cvfe scheme

Notes for the reviewer

The following points need to be discussed:

• When not using default template parameters, then the gridGeometry interface is not backwards compatible. I am not sure if we need to be backwards compatible, because it is probably not yet used very often. If we want to be, then we could move enableHybridCVFE after Traits of we add it to the Traits class --> added to traits
• Think about how to get rid of building scvs for hybrid dofs
• Can we rely on C+20? As a first solution I used ranges to easily iterate over localDofs. In the long term we could introduce a new concept of a container storing just some local dof information. --> even easier in Dune, no need here yet. I also transform it now to return a dof class.
• Naming: I currently use evalElementFluxAndSource and evalElementStorage it seemed to be the most consistent ones. But maybe we find better ones.
• I did not yet implement a new source function interface but I assume that there is a soureAtPos implemented.
• The same for boundary handling. We have to think if it is possible to use the current interface which gets the bcType from scv. Currently I assume that there are ***atPos() functions.

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