make selectionSet input readonly

[iartemiev]

Description of changes:
selectionSet input value accepts array literals (as const). This allows using an array literal for the value as well as with the SelectionSet util type.

const postSelectionSet = ['id', 'title', 'comments.*'] as const

// value
await client.models.Post.list({ selectionSet: postSelectionSet })

// type
type MyPost = SelectionSet<Schema['Post'], typeof postSelectionSet>

This is an additional way to define a custom selection set. The existing inline definition using a regular string array without a const assertion remains available:

await client.models.Post.list({ selectionSet: ['id', 'title', 'comments.*'] })

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[changeset-bot]

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Latest commit: a466af3

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@aws-amplify/amplify-api-next-types-alpha	Patch

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