Creating a GitHub Action to run DRC checks on cells.

This GitHub Action uses Magic to run the SKY130 design rules pulled from
OpenPDKs on all the cells in a standard library.

See the `README.rst` for instructions on how to use.

Signed-off-by: Tim 'mithro' Ansell <tansell@google.com>
Signed-off-by: Mohamed Gaber <mohamed.gaber@efabless.com>