feat(util-waiter): aggregate observed responses in waiter response

[kuhe]

Addresses: aws/aws-sdk-js-v3#6699

Collects a count of observed responses during the polling of a waiter.

code:

import { IAM, waitUntilUserExists } from "@aws-sdk/client-iam";

const iam = new IAM({ region: "us-west-2" });

await waitUntilUserExists(
  {
    client: iam,
    maxWaitTime: 15.001,
  },
  {
    UserName: "echo2",
  }
);

old:

Error [TimeoutError]: {"state":"TIMEOUT","reason":"Waiter has timed out"}

new (when failed):

Error [TimeoutError]: {
	"state":"TIMEOUT",
	"observedResponses":{"404: The user with name echo2 cannot be found.":5},
	"reason":"Waiter has timed out"
}

new (when unauthorized):

Error [TimeoutError]: {
	"state":"TIMEOUT",
	"observedResponses":
		{"403: User: arn:aws:sts::... is not authorized to perform: iam:GetUser on resource: user echo2 because no identity-based policy allows the iam:GetUser action":5},
	"reason":"Waiter has timed out"
}