fix(storage): update instructions for adding external S3 buckets to Amplify

[tiffanynwyeung]

Description of changes:

• Fix permissions policy when adding IAM roles/permissions to an external S3 bucket to correctly mention both <bucket-name>/ as well as <bucket-name>/*
• Update backend.addOutput to specify more options like paths and user group configuration, as well as required Amplify policies in order to access external S3 bucket
• Add different examples for configuring custom authorization rules/user access types
• Update manual Amplify.configure example to match new backend.addOutput example
• Update amplify_outputs.json example to match new backend.addOutput example

Related GitHub issue #, if available:

#8202 and aws-amplify/amplify-ui#6258

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• amplify-cli
• amplify-ui
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[tiffanynwyeung]

Reordered "Guest Users" and "Authenticated Users" examples to match the order listed in the custom auth rules/access types page on the docs

[tiffanynwyeung]

@josefaidt Using Bucket.fromBucketAttributes here instead of Bucket.fromBucketName as it allows for explicit region specification. This is important in the scenario where a bucket being imported exists in a different region from the backend stack; without specifying the region, the outputs will default to the backend stack region and throw an access error.

[ashika112]

Wanted to call out, Amplify Storage Browser in specific will need the buckets to be in same region because of some restriction in IAM IDC and AccessGrants setup. This is only for managed auth use cases though. That said Amplify Storage APIs itself doesnt bother much about region so i guess choosing one over another.

@josefaidt is there any backend best practices that you are aware of for choosing one over an another?

[ashika112]

Good work on this tiffany