feat: exclude OTEL instrumentation via build tag (#770)

* feat: exclude OTEL instrumentation via build tag

* add readme

internal/otel/otel.go

@@ -0,0 +1,12 @@
+//go:build !no_otel
+
+package otel
+
+import (
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/trace"
+)
+
+func Tracer(name string) trace.Tracer {
+	return otel.Tracer(name)
+}

internal/otel/shim.go

@@ -0,0 +1,22 @@
+//go:build no_otel
+
+package otel
+
+import (
+	"context"
+)
+
+type FakeTracer struct{}
+type FakeSpan struct{}
+
+func Tracer(name string) FakeTracer {
+	return FakeTracer{}
+}
+
+func (t FakeTracer) Start(ctx context.Context, _ string) (context.Context, FakeSpan) {
+	return ctx, FakeSpan{}
+}
+
+func (s FakeSpan) End() {
+
+}