Allow selecting backend before running sample

Author: cschleiden

.vscode/launch.json

@@ -3,14 +3,25 @@
   // Hover to view descriptions of existing attributes.
   // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
   "version": "0.2.0",
+  "inputs": [
+    {
+      "id": "backend",
+      "type": "pickString",
+      "description": "Choose a backend",
+      "default": "memory",
+      "options": ["mysql", "sqlite", "redis", "memory"]
+    }
+  ],
   "configurations": [
-
     {
       "name": "Current sample",
       "type": "go",
       "request": "launch",
       "mode": "debug",
-      "program": "${fileDirname}"
+      "program": "${fileDirname}",
+      "args": [
+        "-backend", "${input:backend}",
+      ]
     },
     {
       "name": "Launch simple sample",