Revert "remove slug validations for now"

This reverts commit 7249079688c59b78d04c2266cff2bd1c0ee9d596.
don't require slug for potential project

[#73458302]
add kickoff_tomorrow to project_mailer

[#72945582]
add exact kickoff date to kickoff_tomorrow mailer

[#72945582]
add task to send kickoff_tomorrow mail reminders

[#72945582]
add kickoff_tomorrow scope to projects

[#72945582]
add spec to kickoff_tomorrow project scope

[#72945582]
specify the kickoff_tomorrow spec context better

[#72945582]
fix names in project mailer job

[#72945582]