MM-25263 Add group members to search and get users and create getGroupStats endpoint (#14733)

Add tests for SearchInGroup

model/user_get.go

@@ -12,6 +12,8 @@ type UserGetOptions struct {
 	InChannelId string
 	// Filters the users not in the channel
 	NotInChannelId string
+	// Filters the users in the group
+	InGroupId string
 	// Filters the users group constrained
 	GroupConstrained bool
 	// Filters the users without a team