[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

api4/bleve_test.go

@@ -0,0 +1,32 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package api4
+
+import (
+	"testing"
+
+	"github.com/mattermost/mattermost-server/v5/model"
+)
+
+func TestBlevePurgeIndexes(t *testing.T) {
+	th := Setup(t).InitBasic()
+	defer th.TearDown()
+
+	t.Run("as system user", func(t *testing.T) {
+		_, resp := th.Client.PurgeBleveIndexes()
+		CheckForbiddenStatus(t, resp)
+	})
+
+	t.Run("as system admin", func(t *testing.T) {
+		_, resp := th.SystemAdminClient.PurgeBleveIndexes()
+		CheckOKStatus(t, resp)
+	})
+
+	t.Run("as restricted system admin", func(t *testing.T) {
+		th.App.UpdateConfig(func(cfg *model.Config) { *cfg.ExperimentalSettings.RestrictSystemAdmin = true })
+
+		_, resp := th.SystemAdminClient.PurgeBleveIndexes()
+		CheckForbiddenStatus(t, resp)
+	})
+}