support existing secrets for aws creds

[sh4sh]

What

Partially addresses https://github.com/airbytehq/airbyte/issues/22529 There are helm values to override AWS_SECRET_ACCESS_KEY and AWS_ACCESS_KEY_ID with existing secrets, but at the moment they don't seem to work. I added some logic to support these values.

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• [ ] NO ❌

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Airbyte Code Coverage

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