Move template-field validation out of init for Amazon DataSync operator

[Avcu]

Template fields are rendered only after operators' constructor runs. Therefore, I moved the field validation logic out of __init__ for Amazon DataSync operator. I also updated the unit tests accordingly and run them locally.

• related: Move template-field validation/transformation out of operator __init__ (exemption-list burn-down) #70296 | @shahar1

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[justinpakzad]

Just an fyi - I think you will also need to delete the class path in the validate_operators_init_exemptions.txt file.

[Avcu]

Just an fyi - I think you will also need to delete the class path in the validate_operators_init_exemptions.txt file.

Thank you @justinpakzad, I have updated my PR.

[shahar1]

Great!