Add ability to query which node operators run a certain runtime

##### SUMMARY
Add ability to query which node operators run a certain runtime (e.g. Sapphire).

Consider also adding a query to be able to see which node types (e.g. consensus, paratime, ...) a certain node operator entity runs.

This will be needed for https://github.com/oasisprotocol/explorer/issues/2153.

##### ISSUE TYPE
- Feature Idea