[cmake][deps] Add back accidentally removed option DUMUX_ENABLE_GRIDFORMAT
The newly introduced option DUMUX_ENABLE_GRIDFORMAT was accidentally removed when updating the cmake setup in !3899 (merged). This reintroduces the option.
The newly introduced option DUMUX_ENABLE_GRIDFORMAT was accidentally removed when updating the cmake setup in !3899 (merged). This reintroduces the option.