[DISCUSS] Support *_file and *_cmd suffixes in AirflowConfigParser.getjson()

[singa ser <si...@gmail.com>]

Hi Airflow Devs,

I opened PR #72355 to add support for *_file and *_cmd configuration
suffixes in AirflowConfigParser.getjson(), aligning it with the secret
retrieval pattern across other getter methods in AirflowConfigParser (such
as .get(), .getboolean(), .getint(), etc.).

Currently, getjson() only reads direct values from configuration objects or
environment variables. If a user sets a JSON configuration using *_FILE or
*_CMD suffixes (e.g., AIRFLOW__<SECTION>__<KEY>_FILE or
AIRFLOW__<SECTION>__<KEY>_CMD), getjson() does not evaluate the file path
or command output.

Proposed changes:
- Update AirflowConfigParser.getjson() to evaluate *_file and *_cmd
suffixes when retrieving values.
- Retain full backwards compatibility (fallback to direct key lookup).

PR reference: https://github.com/apache/airflow/pull/72355

Looking forward to your feedback and thoughts!

Best regards,
Shivansh