Optimize entity thumbnail storage

[martastain]

This pull request introduces several enhancements and new functionalities to the thumbnail storage and retrieval system. The most important changes include adding support for original thumbnails, refactoring storage methods, and improving the cleanup process for unused thumbnails.

When an uploaded thumbnail is larger than a defined value (currently hardcoded 600px both width and height) the original is stored in the project storage (server/projects/{project_name}/thumbnails) and a scaled down version is saved to the DB for quick retrieval.

Tasks

• save scaled down version of the image to the database, and the original to the project storage
• support ?original=true in [GET] ..../thumbnail endpoints to retrieve the original image
• implement file deletion in thumbnails cleaner process
• implement "optimize thumbnails" background process that will be executed once (rest?) and handle older "large" thumbnails (separate PR?)

Description of changes

• Added an original parameter to various thumbnail retrieval functions to fetch the original image from storage if available.
• Introduced new methods in ProjectStorage for handling thumbnails, including storing, retrieving, and deleting thumbnail images.
• Updated the clear_thumbnails function to improve the deletion process of old thumbnails, ensuring that only those not referenced in the database are removed.
• Included detailed docstrings and comments for better code readability and maintenance.

These changes collectively enhance the robustness and functionality of the thumbnail management system, making it more efficient and easier to maintain.