Publish JSON schema for airflow.cfg

[Ayush-srivastava504]

This PR adds tooling to generate and validate a JSON Schema for Airflow configuration.

What is included:

• A script to generate a JSON Schema from airflow/config_templates/config.yml
• A validation script to validate airflow.cfg using the generated schema
• A generated schema.json file for IDE support and tooling

Why:

• Enables early detection of invalid or misspelled config options
• Improves IDE autocomplete and validation
• Makes configuration errors visible before runtime

Notes:

• Validation works by parsing airflow.cfg into a dict and validating it against JSON Schema
• This does not change Airflow runtime behavior
• No backward compatibility impact
  Closes Publish JSON schema for airflow.cfg #42850

[Ayush-srivastava504]

I initially added a small validation helper to demonstrate usage of the generated JSON Schema.
After reviewing Airflow’s project structure and static checks, I removed it to avoid import-time side effects and keep the PR scope focused.
This PR now strictly covers schema generation and publication from config.yml.
Validation is intentionally left to external JSON Schema tooling (IDE, CI, pre-commit, etc.).