Cover router should expose used capacity per pool, per product

[roxdanila]

Endpoints interface to be defined with Andreea, and used in the staking pool view table

[mixplore]

#Draft

Used capacity for each pool (overall)

Endpoint route: /staking-pools/capacity

Array<{
    poolId: number;
    usedCapacity: string; // hex convertible to BigNumber
}>

Endpoint route: /staking-pools/:pool-id/capacity

{
    poolId: number;
    usedCapacity: string; // hex convertible to BigNumber
}

Used capacity for each pool product

Endpoint route: /staking-pool/:pool-id/products

Array<{
    productId: number;
    usedCapacity: string; // hex convertible to BigNumber
}>