Make flagging available to anonymous users with an UUID + record username or UUID of flaggers

[teolemon]

Feature Description:

• Public Login: The login on NutriPatrol should be accessible to everyone, even without an OpenFoodFacts account. This is intended to maximize the number of users who can report issues.
• Anonymous Flagging: There is no option for anonymous flagging or flagging with a unique identifier (UUID). This could be added to further encourage reporting.
• Identifier Logs: The identifiers of logged-in users who make reports are not recorded. This could be implemented to recognize user contributions and contact them for quality improvement.

Impact

• Increased Participation: Anonymous flagging allows anyone to report issues, potentially increasing the number of reports and improving data quality.
• Encouraging people with Privacy Concerns to report anyway: The lack of anonymous flagging might deter some users from reporting problems. Adding this option could encourage more reports.
• User Recognition: Recording identifiers of users who make reports (while respecting privacy) could help recognize their contributions and engage them in improving the data quality

Steps to Reproduce

• Access NutriPatrol.
• Observe that login is required
• Try to flag a product and note the lack of an anonymous flagging option.

Expected Behavior

• The login should remain as it is
• An option for anonymous flagging or flagging with a UUID should be added.
• Identifiers of logged-in users who make reports should be recorded.