Fund button - setupOnrampEventListeners util for setting up onSuccess, onEvent and onExit callbacks

[rustam-cb]

What changed? Why?
Added util function setupEventSubscriptions that is used to specify onEvent, onExit and onSuccess callbacks

Notes to reviewers
Example of usage of setupOnrampEventListeners

import { setupOnrampEventListeners } from '@onchainkit/utils';

setupOnrampEventListeners({
  onEvent: (event: EventMetadata) => {
    console.log('Event received', event.eventName);
  },
  onExit: () => {
    console.log('Exit event received');
  },
  onSuccess: () => {
    console.log('Success event received');
  } ,
  host: 'https://somthing.coinbase.com', // Optional: The host of the Coinbase Onramp widget. Defaults to https://pay.coinbase.com.
});

How has it been tested?
Unit tests added

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[alessey]

lgtm