Improve queries to be aware of AccountRegistry entry Id
The Accounts contract has a method Entry to get an account with the signature:
func (_Accounts *AccountsSession) Entry(_idx *big.Int) (common.Address, error)
Currently we only store the address of the entry but not the id which means when we query for new accounts we have to iterate through all the entries which takes a long time.
Proposed improvement: add the Entry Id to the schema of UserEntity and use it during the getNewUsersToAdd function to limit the number of Entry method calls on the AccountsIndex contract to only those Entry which don't have an id in the database.