[PMS] Incorporate waitlist promotion system into Participants page

[taesungh]

For our walk-in hackers, check-in leads will need to be allowed to promote waitlisted hackers as an action on the Participants page.

• Include hackers with intermediate statuses (WAITLISTED, ACCEPTED, WAIVER_SIGNED, CONFIRMED) in the /admin/participants endpoint
• Show Promote action instead of Check In for participants with a WAITLISTED status
• Disable the Promote action for organizers who are not check-in leads
  • Include a tooltip suggesting that only check-in leads are permitted to promote walk-ins
• Disable the Check In action for participants with WAIVER_SIGNED status
  • Include a tooltip suggesting that the hacker must confirm attendance in their portal
  • Will need to be careful with roles and how Implement system to manage status of non-hacker participants #318 ends up
• Allow check-in leads to use the Promote action which shows a modal with a confirmation button and instructions to provide the participant (log into portal, sign waiver, confirm attendance, etc.)
• Allow check-in associates to use /admin/checkin endpoint on CONFIRMED participants
  • Previously considering making only leads able to verify walk-ins, but only leads can promote anyway