Rename "Concierge" role to "Promoter"

[jace]

The "Concierge" role was introduced in #401 to specify an individual responsible for managing logistical operations in a project: booking venues, coordinating travel, and handling participant queries. Concierges have access to contact information of participants (attendees and presenters) as a requirement for their role.

This role has become redundant with the switch to online events, but one specific aspect – managing a mailing list of participants – has taken prominence. This aspect is also an outbound rather than inbound function, so it needs a clearer name: promoter.

#1014 describes promotion of projects. This ticket clarifies that one: promotion is the duty of a promoter, not editor.