Allow arrays values in http_cfg_append

Allow arrays as values for variables that can be declared multiple times. For example:

```
nginx::http_cfg_append:
  set_real_ip_from:
    - "10.0.0.0/24"
    - "31.13.24.0/21"
    - "31.13.64.0/18"
    - "66.220.144.0/20"
    - "69.63.176.0/20"
    - "69.171.224.0/19"
    - "74.119.76.0/22"
    - "103.4.96.0/20"
```

result:

```
  set_real_ip_from 10.0.0.0/24;
  set_real_ip_from 31.13.24.0/21;
  set_real_ip_from 31.13.64.0/18;
  set_real_ip_from 66.220.144.0/20;
  set_real_ip_from 69.63.176.0/20;
  set_real_ip_from 69.171.224.0/19;
  set_real_ip_from 74.119.76.0/22;
  set_real_ip_from 103.4.96.0/20;
```