Add interface for EventReservation in firebase.ts (#695)

* Add interface for EventReservation in firebase.ts

Will add into the wiki after approval

* Change EventReservation to subcollection

Changed EventSlot -> Event

* Adds clarity as there is no longer a need for a "slot"

* Remove reservations list in Event

server/src/data-layer/models/firebase.ts

@@ -130,7 +130,27 @@ export interface BookingChange {
   new_check_out: Timestamp // New check-out timestamp
 }
 
-export interface EventSlot {
+export interface EventReservation {
+  /**
+   * The first name of the user who made this event reservation
+   */
+  first_name: string
+  /**
+   * The last name of the user who made this event reservation
+   */
+  last_name: string
+  /**
+   * The email of the user who made this even reservation
+   */
+  email: string
+  /**
+   * Boolean to check if the user is a member
+   * @example true
+   */
+  is_member: boolean
+}
+
+export interface Event {
   /**
    * The title of this event
    * @example Snowboarding race!