NbSearch Template/Component Reference

### Issue type

**I'm submitting a ...** (check one with "x")

* [ ] bug report
* [x] feature request

### Issue description

**Current behavior:**
Static template.

**Expected behavior:**
Behave more like NbWindowService, accept a template/component reference so we can supply custom controls along with the input.

For my use case, i want to make a toggle with the control when its active to build a custom payload for the search event, in an advanced mode search of my application.