[MM-20979] Add first implementation of the Bleve search engine (#14562)

* [MM-20979] Add first implementation of the Bleve search engine

* Fix i18n

* Migrate searchengine utils tests

* Fix linter

* Don't add allTermsQ if both termQueries and notTermQueries are empty

* Fix test that should work if user is system admin

* Modify naming according to review comments

* Abstract getIndexDir function

* Extracting bleve engine name as a constant

* Merge both Indexer interfaces into one

* Add worker stopped message

* Allow worker to be started/stopped with config change

* Use constants for index names

* Modify test order

* Fix linter

* Trying to unlock the CI

app/app_iface.go

@@ -782,6 +782,7 @@ type AppIface interface {
 	ProcessSlackText(text string) string
 	Publish(message *model.WebSocketEvent)
 	PublishSkipClusterSend(message *model.WebSocketEvent)
+	PurgeBleveIndexes() *model.AppError
 	PurgeElasticsearchIndexes() *model.AppError
 	ReadFile(path string) ([]byte, *model.AppError)
 	RecycleDatabaseConnection()