MM-11782: Make archived channels experimental and off-by-default. (#9281)

* MM-11782: Make archived channels experimental and off-by-default.

* Fix test.

api4/post_test.go

@@ -1273,6 +1273,16 @@ func TestGetPostThread(t *testing.T) {
 func TestSearchPosts(t *testing.T) {
 	th := Setup().InitBasic()
 	defer th.TearDown()
+	experimentalViewArchivedChannels := *th.App.Config().TeamSettings.ExperimentalViewArchivedChannels
+	defer func() {
+		th.App.UpdateConfig(func(cfg *model.Config) {
+			cfg.TeamSettings.ExperimentalViewArchivedChannels = &experimentalViewArchivedChannels
+		})
+	}()
+	th.App.UpdateConfig(func(cfg *model.Config) {
+		*cfg.TeamSettings.ExperimentalViewArchivedChannels = true
+	})
+
 	th.LoginBasic()
 	Client := th.Client
 
@@ -1316,6 +1326,16 @@ func TestSearchPosts(t *testing.T) {
 		t.Fatal("wrong search")
 	}
 
+	th.App.UpdateConfig(func(cfg *model.Config) {
+		*cfg.TeamSettings.ExperimentalViewArchivedChannels = false
+	})
+	
+	posts, resp = Client.SearchPostsIncludeDeletedChannels(th.BasicTeam.Id, "#hashtag", false)
+	CheckNoError(t, resp)
+	if len(posts.Order) != 1 {
+		t.Fatal("wrong search")
+	}
+
 	if posts, resp = Client.SearchPosts(th.BasicTeam.Id, "*", false); len(posts.Order) != 0 {
 		t.Fatal("searching for just * shouldn't return any results")
 	}