HF RL Explorer

Add Elasticsearch metadata extraction support

Add Elasticsearch metadata extraction support: a task in LegoFlow-SWE (Harbor dataset). Both extractors should follow the standard extractor pattern, with init(conf) and extract() methods. extract() must yield records one at a time until exhausted.

The task

Both extractors should follow the standard extractor pattern, with `init(conf)` and `extract()` methods. `extract()` must yield records one at a time until exhausted.

Part of Lego-X/LegoFlow-SWE.