proftpd: add instance json schemas

software/proftpd/instance-input-schema.json

+{
+  "$schema": "http://json-schema.org/draft-04/schema#",
+  "description": "Parameters to instantiate PoFTPd",
+  "additionalProperties": false,
+  "properties": {
+    "port": {
+      "description": "Port number to listen to - default to 8022",
+      "type": "number"
+    }
+  }
+}

software/proftpd/instance-output-schema.json

+{
+  "$schema": "http://json-schema.org/draft-04/schema#",
+  "description": "Values returned by ProFTPd instantiation",
+  "additionalProperties": false,
+  "properties": {
+    "url": {
+      "description": "URL of the SFTP service",
+      "pattern": "^sftp://",
+      "type": "string"
+    },
+    "username": {
+      "description": "Default username",
+      "type": "string"
+    },
+    "password": {
+      "description": "Password for default username",
+      "type": "string"
+    }
+  },
+  "type": "object"
+}

software/proftpd/software.cfg.json

+{
+  "name": "ProFTPd",
+  "description": "ProFTPd as a SFTP server with virtual users",
+  "serialisation": "json-in-xml",
+  "software-type": {
+    "default": {
+      "title": "Default",
+      "description": "ProFTPd, with a default user and users added with command line",
+      "request": "instance-input-schema.json",
+      "response": "instance-output-schema.json",
+      "index": 0
+    }
+  }
+}