CDK: fix license headers and mypy errors

[keu]

Current Behavior

We use pre-commit to validate python code locally, currently, CDK does not pass pre-commit checks, which makes it less usable if usable at all.

Expected Behavior

The code in CDK is properly formatted and pre-commit checks are passed.

Logs

base) ➜  python git:(keu/cdk-base-pydantic-models) ✗ pre-commit run --files airbyte_cdk/sources/config.py
licenseheaders...........................................................Passed
black....................................................................Passed
isort....................................................................Passed
prettier.............................................(no files to check)Skipped
flake8...................................................................Passed
mypy.....................................................................Failed
- hook id: mypy
- exit code: 1

airbyte-cdk/python/airbyte_cdk/sources/config.py: note: In member "schema" of class "BaseConfig":
airbyte-cdk/python/airbyte_cdk/sources/config.py:60:9: error: Returning Any
from function declared to return "Dict[str, Any]"  [no-any-return]
            return schema
            ^
airbyte-cdk/python/airbyte_cdk/sources/abstract_source.py:29: note: In module imported here,
airbyte-cdk/python/airbyte_cdk/sources/__init__.py:1: note: ... from here:
airbyte-cdk/python/airbyte_cdk/sources/utils/schema_helpers.py:13:1: error:
Module 'airbyte_cdk.models' does not explicitly export attribute
'ConnectorSpecification'; implicit reexport disabled  [attr-defined]
    from airbyte_cdk.models import ConnectorSpecification
    ^
airbyte-cdk/python/airbyte_cdk/sources/utils/schema_helpers.py: note: In member "__call__" of class "JsonFileLoader":
airbyte-cdk/python/airbyte_cdk/sources/utils/schema_helpers.py:32:9: error:
Returning Any from function declared to return "Dict[str, Any]"  [no-any-return]
            return json.load(open(uri))
            ^
airbyte-cdk/python/airbyte_cdk/sources/utils/schema_helpers.py: note: In function "resolve_ref_links":
airbyte-cdk/python/airbyte_cdk/sources/utils/schema_helpers.py:47:9: error:
Returning Any from function declared to return "Dict[str, Any]"  [no-any-return]
            return obj
            ^

[augan-rymkhan]

When running mypy check, it gives 46 errors. I opened a new issue for that.