Add JSON schemas for beremiz-runtime.

See merge request nexedi/slapos!1368

software/beremiz-runtime/instance-input-schema.json

+{
+  "$schema": "https://json-schema.org/draft/2019-09/schema",
+  "description": "Parameters to instantiate beremiz-runtime.",
+  "type": "object",
+  "properties": {
+    "runtime_plc_url": {
+      "description": "The network (http / https) address of the gzipped PLC source project program file.",
+      "type": "string",
+      "default": ""
+    }
+  }
+}

software/beremiz-runtime/instance-output-schema.json

+{
+  "$schema": "https://json-schema.org/draft/2019-09/schema",
+  "description": "Values returned by Beremiz-runtime's instantiation.",
+  "additionalProperties": false,
+  "properties": {},
+  "type": "object"
+}

software/beremiz-runtime/software.cfg.json

+{
+  "name": "Beremiz-runtime",
+  "description": "Beremiz-runtime is a headless implementation of Beremiz-ide which is responsible for compiling and running PLC programs.",
+  "serialisation": "xml",
+  "software-type": {
+    "default": {
+      "title": "Default",
+      "software-type": "default",
+      "description": "Default",
+      "request": "instance-input-schema.json",
+      "response": "instance-output-schema.json"
+    }
+  }
+}