[feature] Add instance-stats-randomize config option (#3718)

* [feature] Add `instance-stats-randomize` config option

* don't use cache (overkill)

internal/api/model/instance.go

@@ -17,7 +17,10 @@
 
 package model
 
-import "mime/multipart"
+import (
+	"mime/multipart"
+	"time"
+)
 
 // InstanceSettingsUpdateRequest models an instance update request.
 //
@@ -148,3 +151,11 @@ type InstanceConfigurationEmojis struct {
 	// example: 51200
 	EmojiSizeLimit int `json:"emoji_size_limit"`
 }
+
+// swagger:ignore
+type RandomStats struct {
+	Statuses           int64
+	TotalUsers         int64
+	MonthlyActiveUsers int64
+	Generated          time.Time
+}