/top_proxy does not takes open orders into account

`top_proxy`, computes the voting weight from the object-balance ES index, which does not include open orders. However the voting weight of a proxy takes into account all the balance + open order of the delegated accounts.

Ideally voting_weight should be retrieved from core node as the computation may change (see voting decay BSIP).

Start at the `top_proxy` endpoint and trace how it obtains voting weight from the object-balance ES index. Compare that value with the delegated accounts' balance and open orders, and review whether the core node exposes the authoritative voting weight, including possible voting decay changes. Done means `/top_proxy` accounts for open orders or retrieves the core node's voting weight.

Written by the indexing model from the issue text.