feat(config): add `support-prompt-cache-key` option for OpenAI compatibility

- Introduced a new `support-prompt-cache-key` configuration option to enable optional prompt cache key derivation for supported models.
- Updated relevant API handlers and internal logic to handle the new configuration.
- Enhanced executor workflows to apply prompt cache keys conditionally during request processing.
- Added tests to validate prompt cache key behavior across various scenarios and providers.
- Updated configuration examples and documentation for the new option.

Closes: #4700