This function allows users to sign up. If both username and password meet the requirements: - Updates the username and the corresponding password in the user_accounts dictionary. - Updates the log_in dictionary, setting the value to False. - Returns True. If the username and password fail to meet any one of the following requirements, returns False. - The username already exists in the user_accounts. - The password must be at least 8 characters. - The password must contain at least one lowercase character. - The password must contain at least one uppercase character. - The password must contain at least one number. - The username