Redirus should enable user to specify more configuration options for redirestions

Original problem was connected with openlab instances, which required sticky session:

```
upstream kibehmedx_http {
  ip_hash;
  server 10.100.20.11:80;
}
```

The proposition is to add possibility to define properties hash for the redirection. User should be able to create DSL which describes how properties are converted into nginx configuration.

We already have properties hash which is used to fill `location properties`. This concept can be generalized and used by the DSL.

DSL should allow to create `if` conditions, e.g. if `custom_log_name` param is set then additional section is added to nginx configuration.

/cc @djchrap - any proposition how such DSL can looks like?

Final newline missing.