Fix assignment of template field in __init__ in DataSyncOperator

[romsharon98]

Related: #36484

Set default value for parameters.

cc: @shahar1

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[hussein-awala]

Using a dict as a default value is not a good practice:

>>> def test(i, d={}):
...     d[i] = "something"
...     print(d)
... 
>>> test(1, d={})
{1: 'something'}
>>> test(2, d={})
{2: 'something'}
>>> test(1)
{1: 'something'}
>>> test(2)
{1: 'something', 2: 'something'}