Rewrote IMDS emulator in Go, added unit tests.

sts-agent/go.mod

@@ -0,0 +1,15 @@
+module imds-emulator
+
+go 1.27.1
+
+require (
+	cloud.google.com/go/auth v0.24.1
+	golang.org/x/crypto/x509roots/fallback v0.0.0-20261016151342-0ae6809b7559
+)
+
+require (
+	cloud.google.com/go/compute/metadata v0.9.0 // indirect
+	github.com/googleapis/enterprise-certificate-proxy v0.3.17 // indirect
+	github.com/googleapis/gax-go/v2 v2.26.2 // indirect
+	golang.org/x/sys v0.47.0 // indirect
+)