feat(auth_nocache): support for auth-nocache

* This option can be enabled on OpenVPN clients, to silence warnings like:

```
openvpn[12345]: WARNING: this configuration may cache passwords in memory -- use the auth-nocache option to prevent this
```

Author: dimitry-unified-streaming

openvpn/files/client.jinja

@@ -33,3 +33,7 @@ http-proxy {{ config.http_proxy }}
 {%- if config.auth_user_pass is defined %}
 auth-user-pass {{ config.auth_user_pass }}
 {%- endif %}
+
+{%- if config.auto_nocache is defined %}
+auth-nocache
+{%- endif %}

pillar.example

@@ -282,6 +282,7 @@ openvpn:
       auth_user_pass_content: |
         user
         password
+      auth_nocache: ~
       fast_io: ~
       pull: ~
       tls-client: ~