fix: improve Firestore and Storage rules for anonymous users and legacy data

[KarinePistili]

Review and Improve Firestore and Storage Security Rules

Objective

Review and improve the current Firestore and Firebase Storage security rules to provide proper protection without unnecessarily breaking existing functionality, anonymous users, or legacy data.

Tasks

Anonymous Users

• Allow anonymous users to upload and store the media required by anonymous studies/tests.
• Fix the current permission-denied errors when anonymous users upload media.
• Ensure anonymous access is restricted to the appropriate Storage paths and resources.

Firestore & Storage Rules

• Review all current Firestore and Storage rules and identify unnecessarily restrictive permissions.
• Ensure rules correctly support the current flows for owners, Staff, Participants, and anonymous users.
• Review rules that depend on fields that may not exist in older documents.
• Ensure legacy data remains accessible according to its intended permissions.
• Avoid overly strict assumptions that cause small application changes to break existing functionality.
• Improve the rules' readability, maintainability, and consistency.

[chirag-gupta-07]

@KarinePistili Can I work on this issue?

[chirag-gupta-07]

@KarinePistili Check out the PR.