closes https://github.com/paritytech/polkadot-sdk/issues/426.
related to https://github.com/paritytech/polkadot-sdk/pull/1189.
Would help offchain programs to query if there are unclaimed pages of
rewards for a given era.
The logic could look like below
```js
// loop as long as all era pages are claimed.
while (api.call.stakingApi.pendingRewards(era, validator_stash)) {
api.tx.staking.payout_stakers(validator_stash, era)
}
```
The FRAME development environment provides modules (called "pallets") and support libraries that you can use, modify,
and extend to build the runtime logic to suit the needs of your blockchain.
Ankan
73b9a8391f