Change metadata management

[gy-toxyc]

The purpose of this issue is to improve the metadata manegement currently in use.

Tasks

• [ ] Prepare a proper Auth0 Flows script to just call GY Accounts in order for it to set up the metadata that we want.
• [ ] If this works well, delete the old "Achievements" approach.
• [ ] Prepare a proper model for the current metadata, and a way for it to be scalable without affecting existing users in the future.

In order for this issue to be closed, all tasks should be completed.

[gy-toxyc]

Initial Metadata Model (General)

{
    "gy_messages": {
        // Metadata for GY Messages product.
    },
    "other_product": {
        // Metadata for other GYCODING product.
    }
}