M-step : Update the matrix of working variables Z from beta iterative equation
update_z(df, col_id = "id", target, beta_up, df_id, matrix_id)A dataframe
A character value corresponding to id column name
A character value corresponding to the target variable
A matrix of estimated beta in a specific cluster k
A list of dataframe filter by id levels
A list of design matrices filter by id levels
work_z An up-to-date matrix of working variables Z