Enable setting timeslots according to who is booking.

Is your feature request related to a problem? Please describe.
I spoke with an aesthetician (let's call her Laurie) regarding using Appointment, and she mentioned that she wouldn't be able to use this unless she can set the appointment time on a per-client basis. For example, Client A might take 45 minutes for an appointment, but Client B can take 30 minutes, even if it's the same service (ex: arm hair removal).

Laurie would like to be able to set the amount of time for each client. She also knows beforehand how much time a specific client takes, so she wouldn't have to edit this field, it's mostly set and forget per client.

Describe the solution you'd like
The GA calendar is for general availability, so one solution is to have more than one calendar, but even still, our calendars are locked with a specific appointment duration. So Laurie can set up an "arm hair removal" calendar, but that still wouldn't work for her, as the same service can take longer or shorter durations depending on her client. So then she'd have to create a calendar per client and book them that way. Seems tedious.

This feature request is a bit different: Allow our customers to store profiles of people they want to book with, and then send out bookings with their custom settings.

In this example, Laurie would create a client profile for Client A and set duration at 45 minutes. She would create another client profile for Client B, and set the duration for 30 minutes. Then when she wants them to book with her, she creates a bookable url that takes into consideration these client profiles.

The issue describes client profiles with per-client appointment durations and booking URLs, but names no files, tests, or entry points. Start by mapping the existing calendar, booking, and client models, then define the profile and duration workflow before identifying tests that establish when the feature is complete.