[recnet-api] Follow the person who invites the user (#357)

## Description

Follow the person who invites the user when creating an account

## Related Issue

- #356

## Notes

<!-- Other thing to say -->
N/A

## Test

1. Run local server
2. Create a user by hitting `POST /users/me`
3. Check if there is a following record that followerId = userId and
followingId = inviterId

## Screenshots (if appropriate):

TBA

## TODO

- [x] Clear `console.log` or `console.error` for debug usage
- [ ] Update the documentation `recnet-docs` if needed

apps/recnet-api/src/database/repository/user.repository.ts

@@ -107,14 +107,22 @@ export default class UserRepository {
         select: user.select,
       });
 
-      await prisma.inviteCode.update({
+      const inviteCode = await prisma.inviteCode.update({
         where: { code: createUserInput.inviteCode },
         data: {
           usedById: userInTransaction.id,
           usedAt: new Date(),
         },
       });
 
+      // follow the person who gave the invite code
+      await prisma.followingRecord.create({
+        data: {
+          followedById: userInTransaction.id,
+          followingId: inviteCode.ownerId,
+        },
+      });
+
       return userInTransaction;
     });
   }