…at/Indicator matching (elastic#82546)

## Summary

* Adds logging output for trouble shooting
* Adds an API to be able to configure how many concurrent searches and how many items per search to use

API additions are these two switches:

```
concurrent_searches
items_per_search
```

When you create a rule. You can use the following example to post one or to change the settings to see the performance impact:

```ts
./post_rule.sh ./rules/queries/query_with_threat_mapping_perf.json
```

Without using these two experimental API settings, the functionality is the same as the existing algorithm and only advanced users will be able to set the additional REST settings through this API. If you use the front end after setting the settings, the settings will be reset as that's how the forms code currently works and this will not preserve the settings if afterwards a rule is edited/changed.

Both these API settings should be considered experimental and potentially breakable as we figure out the best performance strategies for indicator matching.

### Checklist

- [x] [Unit or functional tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html) were updated or added to match the most common scenarios