RATIONALE

Before this commit, the display of the appointment front-end views was simple but lacked a proper design.
It implements the new design in all the views, allowing more customization, mainly on the avatar display.
A new view is added to act as an operator selection before the time selection, if some condition is met.
This view display a card view of all available staff users, whereas before the selection was only a name
in a select dropdown. All the views are redesigned and harmonized.

MAIN CHANGES

- NEW OPERATOR SELECT VIEW / FLOW
    - The operator cards are made of a large avatar, the name and function of user, as well as a description (website description, which requires website_partner to be now in the website_appointment dependencies).
    - SEE ALL AVAILABILITIES: on that view, the customer can pick this option to allow all suggested staff users to be used when computing availabilities. At that point, it is the same as a random assign method, but restricted to suggested staff users (the ones on the appointment_type, but after filtering)
    - The view is only active if avatars are activated, at least two users can be selected and if the assign_method is 'chosen'
    - Once a user is selected, we reach the calendar time selection view.
    - This view is called via a new route /<appointment_type_id>/select, that redirects to /<appointment_type_id> if the condition is not met. Also, the time selection view will redirect to this new route if the condition is met.
    - url parameters staff_user_id and see_availabilities manage this flow, and are adequately transmitted through the submissions / actions / links in the appointment process. See commit messages for more details.

- DYNAMIC DESIGN
    A new parameter 'AVATARS_DISPLAY' is set on the appointment_types. Views will display user's details / user's avatar according to this value. On creation of 'custom' or 'work_hours' appointment_types, this parameter will be set to True if the linked user has either an image or a function on their partner.

- NEW DESIGN
    All views are redesigned and harmonized. See commit messages and Figma design on task for more details. Those views are:
    - Appointment Card / List Views
    - Calendar time selection
    - Details of Appointment (Form)
    - Appointment Validation
    Some fields are editable in the front-end editor and have now a placeholder. Some (theme-color matching) helper images are also added if no appointment exist, both in front-end / back-end.

- NAVBAR
    The views receive clickable chevrons if website is installed. There is also a 'all appointments' link that redirects to all available appointments.


Task-2496629