Add default 'aws_conn_id' to SageMaker Operators

The SageMaker Operators not having a default value for aws_conn_id is a pain, we should fix that. See EKS operators for an example: https://github.com/apache/airflow/blob/main/airflow/providers/amazon/aws/operators/eks.py

_Originally posted by @ferruzzi in https://github.com/apache/airflow/pull/21673#discussion_r813414043_

[hsrocks]

Got the intent . Yes can see this problem with few of them individually . Appreciate the details 😃 Will work this out.!!

[ferruzzi]

The problem is that the individual operators also declare the aws_conn without a default value so it isn’t optional, and it won’t fall back to that value:

In [1]: class Foo():
   ...:     def __init__(self, myvar=5):
   ...:         self.myvar = myvar
   ...: 
   ...:     def op(self):
   ...:         return self.myvar
   ...: 
   ...: class Bar(Foo):
   ...:     def __init__(self, myvar):
   ...:         super().__init__(myvar=myvar)
   ...: 

In [2]: Foo().op()
Out[2]: 5

In [3]: Foo(3).op()
Out[3]: 3

In [4]: Bar(2).op()
Out[4]: 2

In [5]: Bar().op()
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-6-06b11a1ebf4e> in <module>
----> 1 Bar().op()

TypeError: __init__() missing 1 required positional argument: 'myvar'

So if we move the defaulting into the child Operators, we don’t have to declare aws_conn_id='default_aws' in every operator use:

In [1]: class Foo:
   ...:     def __init__(self):
   ...:         pass
   ...: 
   ...:     def op(self):
   ...:         return self.myvar
   ...: 
   ...: 
   ...: class Bar(Foo):
   ...:     def __init__(self, myvar=5):
   ...:         self.myvar = myvar
   ...:         super().__init__()
   ...: 

In [2]: Bar(2).op()
Out[2]: 2

In [3]: Bar().op()
Out[3]: 5