Easy implementation for Multiple-UserPools

### Is this feature request related to a new or existing Amplify category?

auth, api

### Is this related to another service?

Custom Authorizer (Lambda)

### Describe the feature you'd like to request

Now we can use multiple UserPools with API Gateway or AppSync, using custom attributes and custom authorizer.
https://www.slideshare.net/AmazonWebServices/deconstructing-saas-deep-dive-into-building-multitenant-solutions-on-aws-arc418r1-aws-reinvent-2018

But it is difficult implementation for many developer. We need easier implementation.
And we need implementation to creating tenants for end-user.

aws-amplify/amplify-category-api#292

### Describe the solution you'd like

I'd like custom workflow or CLI options.

I hope that I could implement multiple user pools architecture more easily using Amplify CLI.

### Describe alternatives you've considered

N/A

### Additional context

_No response_

### Is this something that you'd be interested in working on?

- [ ] 👋 I may be able to implement this feature request
- [ ] ⚠️ This feature might incur a breaking change

The issue names no files, tests, or entry points; start by tracing the Amplify CLI's auth and API category workflows for multiple UserPools and custom Lambda authorizers. Done would require an agreed custom workflow or CLI option that simplifies this architecture and supports tenant creation, with scope clarified against amplify-category-api#292.

Written by the indexing model from the issue text.