[NbCardComponent] Enable / Disable dismiss behavior when clicking outside

### Issue type

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

* [ ] bug report x
* [x] feature request

### Issue description

**Current behavior:**
When an NbCard is open and we click outside, it dismiss

**Expected behavior:**
Enable / Disable dismiss behavior when clicking outside the NbCardComponent

### Other information:

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

Node : v11.9.0
npm: 6.5.0
OS: macOS Catalina 10.15.4
Browser: Chrome 80.0.3987.163 (Build officiel)

```

**Angular, Nebular**
```
Angular : 8.2.1
Nebular : 4.6.0
```