feat(auth): throw extended AuthError for service errors from user pool & id pool

[AllanZhengYP]

Description of changes

• Add an optional metadata property to the base AmplifyError class and AuthError class. So customers can inspect the requestId if an AuthError is caused by a service error response.
• Update the error parser to populate the metadata property when parsing error responses from services. Previously it sets purely internal$metadata property.
• Fix the 2 identity pool APIs(GetId, GetCredentialsForId) to throw AuthError. Previously, the 2 APIs throw the base Error instance.
• Update the unit test for identity pool and user pool APIs to verify they all throw AuthError.

Issue #, if available

Description of how you validated changes

Unit tests

Checklist

• PR description included
• yarn test passes
• Unit Tests are changed or added
• Relevant documentation is changed or added (and PR referenced)

Checklist for repo maintainers

• Verify E2E tests for existing workflows are working as expected or add E2E tests for newly added workflows
• New source file paths included in this PR have been added to CODEOWNERS, if appropriate

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[AllanZhengYP]

The diff of this file is messed up, but I only added the 1st test case