BUG with dependency: SQLAlchemy 1.4.0 for user installation

[lukedyer-peak]

Describe the bug

SQLAlchemy >= 1.4.0 breaks the imports in

great_expectations/great_expectations/dataset/sqlalchemy_dataset.py

Line 42 in 1823447

except ImportError:

This isn't showing up in the tests since the tests pin the version from above whereas the user installation doesn't

great_expectations/setup.py

Line 25 in 1823447

"sqlalchemy": ["sqlalchemy>=1.2"],

The stack trace is from trying to scaffold a new suite is:

...
  File ".../great_expectations/data_context/data_context.py", line 1421, in get_batch
    return self._get_batch_v2(
  File ".../great_expectations/data_context/data_context.py", line 1147, in _get_batch_v2
    return validator.get_dataset()
  File ".../great_expectations/validator/validator.py", line 1431, in get_dataset
    return self.expectation_engine(
  File ".../great_expectations/dataset/sqlalchemy_dataset.py", line 508, in __init__
    self._table = sa.Table(table_name, sa.MetaData(), schema=schema)
AttributeError: 'NoneType' object has no attribute 'Table'

As a work around until the code is upgraded to work with 1.4.0 the version installed should be <1.4.0.