[CDK] Refactor reading JSON inputs for syncs under one shared method

[brianjlai]

Tell us about the problem you're trying to solve

This ticket is a precursor to #18946 . We currently attempt to read in JSON file inputs during connector syncs like configs, configured catalogs, and state. Before tackling that issue, we should clean up the code related to file reads and improve code reuse. The naming of the BaseConnector.read_config() is also not accurate since it is currently being used to read other types of inputs too since its a generic json file reader.

Describe the solution you’d like

We should rename BaseConnector.read_config() to read_json_file() to accurately reflect what it is doing. The existing usages of read_config() should be updated.

The Source.read_state() method should start using this newly renamed read_json_file() to read the state JSON file instead of duplicating all the same file reading logic.

Acceptance Criteria

• When running a check operation on a connector, the operation succeeds with valid json
• When running a read operation on a connector, the operation succeeds with valid json
• When running a read where the configured catalog doesn't exist, an error should be thrown

[maxi297]

This has been solved as part of #20019