Feature Request: Automatic Discord roles

Functionality to automatically give out a certain Discord role for:
- Runners that got a run accepted (runne role)
- Volunteers that got accepted (different Discord role for different volunteer role)

Start by inspecting the repository entry points that handle runner and volunteer acceptance, then check whether Discord integration already exists. Define the role mapping for accepted runners and each volunteer role, and verify that accepted users receive the correct Discord role without changing unrelated assignments.

Written by the indexing model from the issue text.