scripts: add script for listing closed bugs

Script to be used when creating a release. For regular releases this can
be called this way:

$ list_issues.py -f issues.md -s 2019-09-01

Will list all closed issues since september 1st, 2019 and will create a
markdown file with all issues that can be added as is to the release
notes.

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