meta: VS Code: add "Git: Always Sign Off" setting

VS Code setting to auto signoff commits.
This also corresponds to our GitHub Web workflow.

Signed-off-by: Andrey Butirsky <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/16540
Signed-off-by: Hauke Mehrtens <[email protected]>

.vscode/settings.json

@@ -0,0 +1,3 @@
+{
+    "git.alwaysSignOff": true
+}