AlignedLattice: boundary condition per direction

[nilsvu]

Proposed changes

Allows to specify a different boundary condition in each direction of the AlignedLattice, just like the rectilinear domains (Interval/Rectangle/Brick).

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Further comments

[nilsvu]

@nilsdeppe mind taking a look at this one too? It's doing the same as #5898 in terms of boundary conditions for AlignedLattice. We might even be able to merge the AlignedLattice features into Rectilinear, but that's a bit more work that I haven't attempted.

[nilsdeppe]

LGTM!

In the future could you please try to keep things like renames of VolumeDim -> Dim in separate commits to make it easier to review?

[nilsvu]

Yes I should've done that in a separate commit