Refactor Get/Create Direct Channel into one function (#9867)

* refactor GetDirectChannel and CreateDirectChannel in one function

* remove CreateDirectChannel plugin api and update GetDirectChannel and GetGroupChannel plugin api

* update tests

api4/apitestlib.go

@@ -426,7 +426,7 @@ func (me *TestHelper) CreateDmChannel(user *model.User) *model.Channel {
 	utils.DisableDebugLogForTest()
 	var err *model.AppError
 	var channel *model.Channel
-	if channel, err = me.App.CreateDirectChannel(me.BasicUser.Id, user.Id); err != nil {
+	if channel, err = me.App.GetOrCreateDirectChannel(me.BasicUser.Id, user.Id); err != nil {
 		mlog.Error(err.Error())
 
 		time.Sleep(time.Second)

api4/channel.go

@@ -339,7 +339,7 @@ func createDirectChannel(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	sc, err := c.App.CreateDirectChannel(userIds[0], userIds[1])
+	sc, err := c.App.GetOrCreateDirectChannel(userIds[0], userIds[1])
 	if err != nil {
 		c.Err = err
 		return

api4/post_test.go

@@ -410,7 +410,7 @@ func TestCreatePostAll(t *testing.T) {
 
 	user := model.User{Email: th.GenerateTestEmail(), Nickname: "Joram Wilander", Password: "hello1", Username: GenerateTestUsername(), Roles: model.SYSTEM_USER_ROLE_ID}
 
-	directChannel, _ := th.App.CreateDirectChannel(th.BasicUser.Id, th.BasicUser2.Id)
+	directChannel, _ := th.App.GetOrCreateDirectChannel(th.BasicUser.Id, th.BasicUser2.Id)
 
 	ruser, resp := Client.CreateUser(&user)
 	CheckNoError(t, resp)