add tracer enabled status

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

tracer/noop.go

@@ -20,6 +20,10 @@ func (t *noopTracer) Spans() []Span {
 
 var uuidNil = uuid.Nil.String()
 
+func (t *noopTracer) Enabled() bool {
+	return t.opts.Enabled
+}
+
 func (t *noopTracer) Start(ctx context.Context, name string, opts ...SpanOption) (context.Context, Span) {
 	options := NewSpanOptions(opts...)
 	span := &noopSpan{