.vscode: wire buildifier to bazel target

Change-Id: I5785096f0f26d262f536e5ea49a0fea41d5b5c10
Reviewed-on: https://review.monogon.dev/c/monogon/+/4491
Tested-by: Jenkins CI
Reviewed-by: Leopold Schabel <leo@monogon.tech>
diff --git a/.vscode/settings.json b/.vscode/settings.json
index 6224c63..5fdb473 100644
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -23,5 +23,6 @@
         "bazel-testlogs/**": true,
         ".bazeldnf/**": true,
     },
-    "bazel.executable": "tools/bazel"
+    "bazel.executable": "tools/bazel",
+    "bazel.buildifierExecutable": "@buildifier_prebuilt//:buildifier",
 }
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