feat: Update proxy implementation and add SSL configuration

[anmaslov]

This PR adds SSL configuration options to address certificate verification issues when connecting to downstream APIs. The changes allow users to configure SSL behavior through environment variables, which is particularly useful when working with corporate firewalls, proxies, or self-signed certificates.

Summary of Changes:

• Added SSL_VERIFY environment variable to enable/disable SSL certificate verification (defaults to true)
• Added CA_BUNDLE_PATH environment variable to specify custom CA bundle for SSL verification
• Updated the OpenAI client to use custom SSL context based on these configuration options
• Added a new /ssl-config endpoint to check current SSL configuration
• Updated README with documentation about SSL configuration options and troubleshooting
• Added a test file test_ssl_config.py to verify SSL configuration handling

Environment Variables:

• SSL_VERIFY: Enable/disable SSL certificate verification (default: true)
• CA_BUNDLE_PATH: Path to custom CA bundle for SSL verification (optional)

These changes should resolve SSL certificate errors like CERTIFICATE_VERIFY_FAILED that users may encounter in certain network environments.

[fuergaosi233]

Why do we need to add this feature? Ordinary users may not need this 🤔