S3 destination: update spec regarding certification checklist

[sashaNeshcheret]

All fields in spec should have the following:

• required fields should be marked with an asterisk (eg. "Authentication *");
• optional fields should be appended with "(Optional)" (eg. "End Date (Optional)" )

Input fields should have following order:

1. Name *
2. Authentication *
3. All other required fields
4. Any optional fields

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