Set User Agent for FFmpeg calls (#4555)

* Set User Agent for FFmpeg calls

* Allow to use shell-like string args

* Add test for arg as string with space

.vscode/launch.json

@@ -0,0 +1,12 @@
+{
+  "version": "0.2.0",
+  "configurations": [
+    {
+      "name": "Python: Launch Frigate",
+      "type": "python",
+      "request": "launch",
+      "module": "frigate",
+      "justMyCode": true
+    }
+  ]
+}