run-drc-for-cell-gds-using-magic: Add action.yml

By adding an `action.yml` the fact that the action is using docker is
hidden and allows us to convert to a javascript action in the future if
we want.

It also makes handing over the inputs nicer and makes it easier to move
between container registries if needed.

Signed-off-by: Tim 'mithro' Ansell <tansell@google.com>