fix(visitor_mailer): support #guest_list ical_uid lookup (PPT-2375)

drivers/place/staff_api.cr

@@ -993,9 +993,13 @@ class Place::StaffAPI < PlaceOS::Driver
     JSON.parse(response.body)
   end
 
-  def event_guests(event_id : String, system_id : String)
+  def event_guests(event_id : String, system_id : String, ical_uid : String? = nil)
     logger.debug { "getting guests for event #{event_id} in system #{system_id}" }
-    response = get("/api/staff/v1/events/#{event_id}/guests?system_id=#{system_id}", headers: authentication)
+    params = URI::Params.build do |form|
+      form.add "system_id", system_id
+      form.add "ical_uid", ical_uid.to_s if ical_uid.presence
+    end
+    response = get("/api/staff/v1/events/#{event_id}/guests?#{params}", headers: authentication)
     raise "issue getting guests for event #{event_id}: #{response.status_code}" unless response.success?
     JSON.parse(response.body)
   end

drivers/place/visitor_mailer.cr

@@ -720,7 +720,7 @@ class Place::VisitorMailer < PlaceOS::Driver
       end
     end
 
-    guests = staff_api.event_guests(details.event_id, details.system_id).get.as_a
+    guests = staff_api.event_guests(details.event_id, details.system_id, details.event_ical_uid).get.as_a
     send_booking_changed_emails(
       guests,
       host,

drivers/place/visitor_mailer_spec.cr

@@ -131,7 +131,7 @@ class StaffAPIMock < DriverSpecs::MockDriver
     ]
   end
 
-  def event_guests(event_id : String, system_id : String)
+  def event_guests(event_id : String, system_id : String, ical_uid : String? = nil)
     [
       {
         email:          "visitor@external.com",