Feat/uploading file

[gamal1osama]

This pull request introduces several enhancements to the file upload functionality, focusing on improved validation, error handling, and file management. The main changes include stricter file validation with detailed response signals, chunked asynchronous file uploads, and better organization for uploaded files by project. Additionally, new configuration options and supporting utilities were added.

File upload and validation improvements:

• Added detailed file validation in DataController, including checks for allowed types and file size, returning specific response signals for each outcome.
• Implemented chunked, asynchronous file saving using aiofiles in the /upload/{project_id} route, improving performance and reliability for large files.

File and project organization:

• Added ProjectController to manage per-project directories and ensure files are saved in the correct location with unique, sanitized filenames.
• Updated .gitignore and asset directory structure to support file uploads and prevent local files from being tracked.

Configuration and utilities:

• Introduced new environment variables and settings for file chunk size and clarified file size units in .env.example and config.py.
• Added a utility to generate random strings for unique filenames in BaseController.

These changes collectively make file uploads more robust, secure, and scalable.