Uploading images into the folder.

# Objective

Implement functionality that allow users to upload image files. The images should be stored in a specified folder in the mongoDB.

# Requirements:

- allow users to upload image files.
- Ensure that each image is linked to its folder by storing a folder_id in the database.

# Steps to Implement:

1. Create a `POST` endpoint `/images/upload`.
2. Accept multipart form data with the image file and metadata fields.
3. Check if the folder_id exists in the folders collection.
4. Link the image to the folder by referencing the folder_id.