Make nb-select work properly with autocomplete from HTML

### Issue type

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

* [ ] bug report
* [X] feature request

### Issue description

**Current behavior:**
nb-select does not handle the autocomplete functionality from HTML.

**Expected behavior:**
This would be useful in a HTML such as a country selection, state selection etc.

**Steps to reproduce:**
```

Select
Canada
United States

```

### Other information:

**npm, node, OS, Browser**
```

```

**Angular, Nebular**
```
Angular: 9.1.0
Nebular: 5.0.0
```