[Enhancement] Add docstring with description, params, and return

[Dario0731]

🛠 Issue: Add docstring with description, params, and return

📌 Description

Add docstring with description, params, and return on every function on : contracts\user_management\src\functions\rbac.rs
Use the next template:

/// Brief description: explains what the function does.
///
/// # Arguments
///
/// * param1 - Explanation of the first parameter (If needed).
/// * param2 - Explanation of the second parameter (If needed).
///
/// # Returns
///
/// * Result<T, E> - What the function returns, with description of Ok and Err.

[big14way]

assign this issue to me i am a fellow

[Hallab7]

I will like to work on this issue