Agree and implement version support for GROMACS 2021
As in #2899, we need to pick the minimum versions of any compilers/libraries/runtimes we wish to support in GROMACS 2021, e.g. C++ std, cmake, CUDA, oneAPI, gcc/icc/clang. We were a little pushy with such versions for GROMACS 2020, so my suggest is that we change very few of our minimum requirements (except declaring any requirements for things newly supported, like perhaps oneAPI). Of course, we should plan to test and support newer versions of existing things.