refactor(sidecarassets): rename internal/sidecar to internal/sidecarassets

internal/sidecarassets/embed_stub.go

@@ -0,0 +1,10 @@
+//go:build !withsidecar
+
+package sidecarassets
+
+var embeddedJAR []byte
+
+// IsPlaceholder reports whether the binary was built without the real
+// sidecar JAR embedded. Build with `make sanderling` (which passes
+// -tags withsidecar) to embed the real fat JAR.
+func IsPlaceholder() bool { return true }