add metrics for dns

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

semconv/cache.go

@@ -0,0 +1,14 @@
+package semconv
+
+var (
+	// CacheRequestDurationSeconds specifies meter metric name
+	CacheRequestDurationSeconds = "micro_cache_request_duration_seconds"
+	// CacheRequestLatencyMicroseconds specifies meter metric name
+	CacheRequestLatencyMicroseconds = "micro_cache_request_latency_microseconds"
+	// CacheRequestTotal specifies meter metric name
+	CacheRequestTotal = "micro_cache_request_total"
+	// CacheRequestInflight specifies meter metric name
+	CacheRequestInflight = "micro_cache_request_inflight"
+	// CacheItemsTotal specifies total cache items
+	CacheItemsTotal = "micro_cache_items_total"
+)