Matrix user names should not include first and last name

[malemburg]

See https://github.com/EuroPython/ep-matrix/blob/epcon_auth/epcon_auth_provider/epcon_auth_provider.py#L226

The auth mechanism currently uses return strip_accents(f"{first_name}.{last_name}.{username}".lower())

This should be return strip_accents(f"{username}".lower()) and would then also avoid issues with accents, spaces, etc.

[fpierfed]

Fixed by using the epcon username.