NbAuthStrategy: setOptions replace config with default value

### Issue type

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

* [x ] bug report
* [ ] feature request

### Issue description

**Current behavior:**
NbAuthStrategyOptions replaced by the default config

**Expected behavior:**
NbAuthStrategyOptions should be merged with already passed options

**Steps to reproduce:**

1. Configure NbAuthModule with auth options
2. Add some property during runtime