feat(api-graphql): alias authMode identityPool -> iam

[iartemiev]

Description of changes

• support authMode: 'identityPool', which is an alias for 'iam'

Description of how you validated changes

• added unit tests

Checklist

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

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