Refactor file management system

[lucassousaf]

The current management of files (images, CVs, etc) have a few problems that can be a problem from both maintenance and database performance in the future:

• Some images for certain entities (stakeholder, event and organisation) store their images in base64 format in the database. Other entities store their images directly in Google Cloud Storage (GCS).
• In this case we store the full URL including the bucket-name in the database. That is not a good idea if you want to change buckets or storage without affecting the existing images. Ideally the bucket-name should be a system configuration that is used at runtime to upload and serve the images and not be stored in the database.
• GPML is using a single GCS bucket to store the images and files for both test and production environment.

The idea is to centralize the images management in a way that:

• All files are stored in GCS.
• Each environment has its own bucket.
• All images/files metadata will be stored in a generic entity named File . This entity will hold metadata such as object_key, extension, filename, created_at and last_modified_at.

[joseAyudarte91]

Leaving this issue opened to perform some post-migration clean-up tasks.