build: Add vscode workspace settings

Without this the language server can't handle tests/e2e_tests.go
from sigstore#128

Signed-off-by: Jussi Kukkonen <jkukkonen@google.com>

Author: jku

.vscode/settings.json

@@ -0,0 +1,3 @@
+{
+    "go.buildTags": "e2e",
+}