Implement File Writing Function

[emmalgs]

What it is

Implement a function in the FileSystemService to write user data to a new file using the FileSystem module.

Context

Writing user data files is required when creating new users.

Acceptance Criteria

• A function named writeFile is defined in the FileSystemService module.
• The function accepts user data and an optional user ID (to determine the file name) as parameters.
• The function writes the provided data to a new JSON file (based on the user ID) using fs.writeFile.