feat(run): add OS variable to use case context (#3)

Author: MarcScheib

README.md

@@ -317,6 +317,7 @@ All steps are working with a context object that is empty initially. Whenever
 a use case starts, the context is filled with the following properties.
 Throughout execution, steps can add or modify properties in the context object.
 
+- `OS`: the operating system where the CLI is executed on; represents the result of [`process.platform`](https://nodejs.org/api/process.html#process_process_platform)
 - `WORKSPACE_PATH`: the absolute path to the workspace
 - `WORKING_DIR`: the absolute path to the working directory, see [Workspace structure](#workspace-structure)
 - `SERVERS`: the list of all servers, see [Server configuration](#server-configuration)

assets/templates/config/use-cases/check-requirements.json

@@ -4,6 +4,11 @@
   "name": "Check requirements",
   "description": "This use case checks the requirements to develop locally.",
   "steps": [
+    {
+      "type": "FORMULA",
+      "description": "Print OS info",
+      "formula": "console.log(`Running on ${OS}`)"
+    },
     {
       "type": "COMMAND",
       "description": "Execute commands",