first stab on bill model

db/booking.ts

@@ -2,7 +2,7 @@ import * as mongoose from 'mongoose'
 import { v4 as uuidv4 } from 'uuid'
 import { dateFormatBackend, getDays } from '../helpers/date'
 import { BookerDocument } from './booker'
-import { BOOKING_STATUS } from './bookingStatus'
+import { BOOKING_STATUS } from './enums'
 
 export interface BookingDocument
   extends mongoose.Document,
@@ -56,6 +56,11 @@ const BookingSchema = new mongoose.Schema<BookingDocument>(
     purpose: { type: String, required: false },
     org: { type: String, required: false },
     destination: { type: String, required: false },
+    bill: {
+      type: mongoose.Schema.Types.ObjectId,
+      ref: 'bill',
+      required: false,
+    },
   },
   {
     timestamps: true,