allow config for callbaks and some fixes

* only complain about ini deprecation if value is set
 * set plugin config for stdout and other types
 * updated plugin docs, moved several plugins to new config
 * finished ssh docs
 * fixed some issues seen in plugins while modifying docs
 * placeholder for 'required'
 * callbacks must use _plugin_options as _options already in use

lib/ansible/plugins/connection/network_cli.py

@@ -28,6 +28,11 @@ DOCUMENTATION:
       private_key_file:
         description:
             - Key or certificate file used for authentication
+        ini:
+            - section: defaults
+              key: private_key_file
+        env:
+            - name: ANSIBLE_PRIVATE_KEY_FILE
         vars:
             - name: ansible_private_key_file
       timeout: