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

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

* Fix test.

app/post.go

@@ -648,7 +648,7 @@ func (a *App) DeletePostFiles(post *model.Post) {
 
 func (a *App) SearchPostsInTeam(terms string, userId string, teamId string, isOrSearch bool, includeDeletedChannels bool) (*model.PostSearchResults, *model.AppError) {
 	paramsList := model.ParseSearchParams(terms)
-	includeDeleted := includeDeletedChannels && *a.Config().TeamSettings.ViewArchivedChannels
+	includeDeleted := includeDeletedChannels && *a.Config().TeamSettings.ExperimentalViewArchivedChannels
 
 	esInterface := a.Elasticsearch
 	if license := a.License(); esInterface != nil && *a.Config().ElasticsearchSettings.EnableSearching && license != nil && *license.Features.Elasticsearch {