Annotations: Adds tags endpoint (#36199)

* Annotations: Adds tags endpoint

* Chore: fixes sql  statement

* Refactor: adds count to the api

* Chore: changes after PR comments

* Refactor: changes after PR comments

pkg/services/sqlstore/annotation_test.go

@@ -251,5 +251,47 @@ func TestAnnotations(t *testing.T) {
 			require.NoError(t, err)
 			assert.Empty(t, items)
 		})
+
+		t.Run("Should find tags by key", func(t *testing.T) {
+			result, err := repo.FindTags(&annotations.TagsQuery{
+				OrgID: 1,
+				Tag:   "server",
+			})
+			require.NoError(t, err)
+			require.Len(t, result.Tags, 1)
+			require.Equal(t, "server:server-1", result.Tags[0].Tag)
+			require.Equal(t, int64(1), result.Tags[0].Count)
+		})
+
+		t.Run("Should find tags by value", func(t *testing.T) {
+			result, err := repo.FindTags(&annotations.TagsQuery{
+				OrgID: 1,
+				Tag:   "outage",
+			})
+			require.NoError(t, err)
+			require.Len(t, result.Tags, 2)
+			require.Equal(t, "outage", result.Tags[0].Tag)
+			require.Equal(t, "type:outage", result.Tags[1].Tag)
+			require.Equal(t, int64(1), result.Tags[0].Count)
+			require.Equal(t, int64(1), result.Tags[1].Count)
+		})
+
+		t.Run("Should not find tags in other org", func(t *testing.T) {
+			result, err := repo.FindTags(&annotations.TagsQuery{
+				OrgID: 0,
+				Tag:   "server-1",
+			})
+			require.NoError(t, err)
+			require.Len(t, result.Tags, 0)
+		})
+
+		t.Run("Should not find tags that do not exist", func(t *testing.T) {
+			result, err := repo.FindTags(&annotations.TagsQuery{
+				OrgID: 0,
+				Tag:   "unknown:tag",
+			})
+			require.NoError(t, err)
+			require.Len(t, result.Tags, 0)
+		})
 	})
 }