Issue search support elasticsearch (#9428)

* Issue search support elasticsearch

* Fix lint

* Add indexer name on app.ini

* add a warnning on SearchIssuesByKeyword

* improve code

vendor/github.com/olivere/elastic/v7/suggester.go

@@ -0,0 +1,15 @@
+// Copyright 2012-present Oliver Eilhard. All rights reserved.
+// Use of this source code is governed by a MIT-license.
+// See http://olivere.mit-license.org/license.txt for details.
+
+package elastic
+
+// Represents the generic suggester interface.
+// A suggester's only purpose is to return the
+// source of the query as a JSON-serializable
+// object. Returning a map[string]interface{}
+// will do.
+type Suggester interface {
+	Name() string
+	Source(includeName bool) (interface{}, error)
+}