Add delegator statistics: unique total in active committee (Nova) [medium]

[begonaalvarezd]

Description

Priority: medium

This is part 2 of 2 statistics we would like to have for delegators. The idea is to have how many unique delegators there are in the active committee

The 2 parts are:

1. unique total (done already)
2. unique total in active committee

Afaik, this needs an INX endpoint

Motivation

Improve statistics to accomodate to new IOTA 2.0 features, like delegator statistics

Requirements

Open questions (optional)

Are you planning to do it yourself in a pull request?

No.