Add/update executive director posting in Careers section

We have the link for the combo Delphi+CMU executive director role!

https://cmu.wd5.myworkdayjobs.com/CMU/job/Pittsburgh-PA/Executive-Director-of-the-Delphi-Research-Group---Strategic-Coordinator-of-Public-Health-Research-Initiatives_2018952

We should:
- [x] update the exec director entry on the careers page
- [x] add a carousel entry for this position