[#2] tagging: Add grpc and context methods

Signed-off-by: Dmitrii Stepanov <d.stepanov@yadro.com>

tagging/context.go

@@ -0,0 +1,21 @@
+package tagging
+
+import "context"
+
+type tagContextKeyType struct{}
+
+var currentTagKey = tagContextKeyType{}
+
+func ContextWithIOTag(parent context.Context, ioTag string) context.Context {
+	return context.WithValue(parent, currentTagKey, ioTag)
+}
+
+func IOTagFromContext(ctx context.Context) (string, bool) {
+	if ctx == nil {
+		panic("context must be non nil")
+	}
+	if tag, ok := ctx.Value(currentTagKey).(string); ok {
+		return tag, true
+	}
+	return "", false
+}