ci: various set_assignee fixes

Cleanup of script and change how we assign PR in general:

Make sure that when multiple areas are changed, including platform or
driver changes, we set assignee of the general areas and not the
platform maintainers. For example, if I change 100 SoC files and touch
the kernel file, the assignee is set to the kernel maintainer.

First, we should as much possible try and split such changes and not
have common area changes with platform changes at the same time. Second,
it is important that such changes which affect everyone are reviewed and
approved by the maintainer of the general areas rather than leave them
to the platform maintainer.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>