adding missing file for transport wrapper

pkg/plugin/definition/transport.go

@@ -0,0 +1,18 @@
+package definition
+
+import (
+	"context"
+	"net/http"
+)
+
+// TransportWrapper is a plugin that wraps an http.RoundTripper,
+// allowing modification of outbound requests (like adding auth).
+type TransportWrapper interface {
+	// Wrap takes a base transport and returns a new transport that wraps it.
+	Wrap(base http.RoundTripper) http.RoundTripper
+}
+
+// TransportWrapperProvider defines the factory for a TransportWrapper.
+type TransportWrapperProvider interface {
+	New(ctx context.Context, config map[string]any) (TransportWrapper, func(), error)
+}