🐛 source smartsheets: fix error getting optional metadata_fields on existing configs

[pedroslopez]

What

Following up on #26991, this PR resolves an issue introduced in v1.1.0 (#22382) when accessing metadata_fields on an existing connection that didn't have the field defined. This is an optional field that is ok to be unset.

Traceback (most recent call last):
  File "/airbyte/integration_code/main.py", line 13, in <module>
    launch(source, sys.argv[1:])
  File "/usr/local/lib/python3.9/site-packages/airbyte_cdk/entrypoint.py", line 156, in launch
    for message in source_entrypoint.run(parsed_args):
  File "/usr/local/lib/python3.9/site-packages/airbyte_cdk/entrypoint.py", line 91, in run
    yield from map(AirbyteEntrypoint.airbyte_message_to_string, self.check(source_spec, config))
  File "/usr/local/lib/python3.9/site-packages/airbyte_cdk/entrypoint.py", line 112, in check
    check_result = self.source.check(self.logger, config)
  File "/usr/local/lib/python3.9/site-packages/airbyte_cdk/sources/abstract_source.py", line 84, in check
    check_succeeded, error = self.check_connection(logger, config)
  File "/airbyte/integration_code/source_smartsheets/source.py", line 17, in check_connection
    sheet = SmartSheetAPIWrapper(config)
  File "/airbyte/integration_code/source_smartsheets/sheet.py", line 18, in __init__
    self._metadata = config["metadata_fields"]
KeyError: 'metadata_fields'

How

Get default empty list value if field is not set on the config
This also unpins the version on cloud

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[pedroslopez]

/test connector=connectors/source-smartsheets

🕑 connectors/source-smartsheets https://github.com/airbytehq/airbyte/actions/runs/5194637747
✅ connectors/source-smartsheets https://github.com/airbytehq/airbyte/actions/runs/5194637747
Python tests coverage:

Name                             Stmts   Miss  Cover
----------------------------------------------------
source_smartsheets/source.py        13      0   100%
source_smartsheets/__init__.py       2      0   100%
source_smartsheets/sheet.py         87      4    95%
source_smartsheets/streams.py       37      4    89%
----------------------------------------------------
TOTAL                              139      8    94%

Build Passed

Test summary info:

=========================== short test summary info ============================
SKIPPED [1] ../usr/local/lib/python3.9/site-packages/connector_acceptance_test/tests/test_core.py:100: The previous and actual specifications are identical.
SKIPPED [1] ../usr/local/lib/python3.9/site-packages/connector_acceptance_test/tests/test_core.py:598: The previous and actual discovered catalogs are identical.
SKIPPED [1] ../usr/local/lib/python3.9/site-packages/connector_acceptance_test/tests/test_core.py:695: This tests currently leads to too much failures. We need to fix the connectors at scale first.
================= 39 passed, 3 skipped, 41 warnings in 28.71s ==================