adds a pre-commit config

To use this run pre-commit install in your module root. Only files modified in the to-be-made commit are checked. You can also run checks unconditionally like this pre-commit run -a yapf|clang-format The clang-format one actually uses a binary wheel distribution of clang-format, which is really nice. We should also check to upgrade to clang-format 13 when we have fewer branches ongoing. Maybe yapf 0.31 too. Ping @ag-ohlberger/dune-community since I cannot request a review from a (sub-)group.