feat: add configuration form for My Bookings button

Problem

The "My Bookings" button link was hardcoded directly into the template openy-repeat-schedule-dashboard.html.twig, making it impossible to configure per-site without editing the theme or template. This limits the reusability of the distribution across multiple sites with different booking URLs.

Solution

A configuration form was introduced under /admin/openy/settings/openy-repeat, allowing site administrators to define the Schedule Booking URL via the UI.

• The link is stored in configuration (openy_repeat.settings) and passed to the template via hook_preprocess_openy_repeat_schedule_dashboard().
• The template now uses the dynamic value of {{ schedule_booking_url }} instead of a hardcoded URL.

This makes the booking link customizable per site and improves the flexibility and maintainability of the module.

changed title from [ITCP-304] Add configuration form for My Bookings button to feat: add configuration form for My Bookings button

mentioned in merge request openy_carnation!109 (merged)

assigned to @shuklina

requested review from @podarok

approved this merge request

merged