Add estimated_inbound and estimated_outbound values in balance requests

[alter-eggo]

Is your feature request related to a problem? Please describe.
To get immediately available balance that user can send we need to do 2 requests - for balance and mempool transactions, so
available balance = total balance - locked balance - outbound txs value
It would be great to do only 1 request to get available balance

Describe the solution you'd like
There is already estimated_balance in the balance request which uses inbound/outbound mempool txs values in calc.
so it would be great to add estimated_inbound and estimated_outbound values in balance request response