feat: use mongodb official driver instead of mgo (#1782)

* wip: backup

* wip: backup

* wip: backup

* backup

* backup

* backup

* add more tests

* fix wrong dependency

* fix lint errors

* remove test due to data race

* add tests

* fix test error

* add mon.Model

* add mon.Model unmarshal

* add monc

* add more tests for monc

* add more tests for monc

* add docs for mon and monc packages

* fix doc errors

* chhore: add comment

* chore: fix test bug

* chore: refine tests

* chore: remove primitive.NewObjectID in test code

* chore: rename test files for typo

core/stores/mon/options_test.go

@@ -0,0 +1,18 @@
+package mon
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestSetSlowThreshold(t *testing.T) {
+	assert.Equal(t, defaultSlowThreshold, slowThreshold.Load())
+	SetSlowThreshold(time.Second)
+	assert.Equal(t, time.Second, slowThreshold.Load())
+}
+
+func TestDefaultOptions(t *testing.T) {
+	assert.Equal(t, defaultTimeout, defaultOptions().timeout)
+}