feat(firebase): allow to declare collections and their schema

[ghusse]

Linked to CU-2d8jkm5

Definition of Done

General

• Write an explicit title for the Pull Request, following Conventional Commits specification
• Test manually the implemented changes
• Validate the code quality (indentation, syntax, style, simplicity, readability)
• Ensure that Types have been updated according to your changes (if needed)

Security

• Consider the security impact of the changes made

[forest-bot]

Task linked: CU-2d8jkm5 Story #3 - Add declaration for collection fields