chore: move utils.Chain into chain-helpers package

[ntn-x2]

Fixes https://github.com/KILTprotocol/ticket/issues/2869.

We discussed about moving the chain-helpers module into the utils package. but after checking both packages, I found it would be more logic to simply move the chainy stuff of the utils package under the Blockchain namespace of the chain-helpers.

The new utility functions to parse blocks and retrieve extrinsics, can be accessed as in the following snippet:

import { Blockchain } from "@kiltprotocol/chain-helpers"

const extrinsic = await Blockchain.retrieveExtrinsicFromBlock(
    blockNumber,
    ({ events }) =>
      events.some(
        (event) =>
          api.events.publicCredentials.CredentialStored.is(event) &&
          event.data[1].toString() === credentialId
      ),
    api
  )

I made the input api: ApiPromise optional, so that it would allow people to use the default returned by ConfigService.get('api') if they need, but internally it needs to be retrieved once and passed along.

[rflechtner]

I like it!