feat: add email to notification and otp

apps/edr-freight-api/src/modules/otp/otp.entity.ts

@@ -10,10 +10,19 @@ import { BaseEntity } from "@edr/api-common";
   name: "otp_verifications",
 })
 export class OtpVerification extends BaseEntity{
+  // Exactly one of phone/email is set per row — the channel the code was sent
+  // through.
   @Column({
     unique: true,
+    nullable: true,
   })
-  phone!: string;
+  phone?: string;
+
+  @Column({
+    unique: true,
+    nullable: true,
+  })
+  email?: string;
 
   @Column()
   otp!: string;