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/search_queries_slice.go

@@ -0,0 +1,53 @@
+// 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
+
+// SliceQuery allows to partition the documents into several slices.
+// It is used e.g. to slice scroll operations in Elasticsearch 5.0 or later.
+// See https://www.elastic.co/guide/en/elasticsearch/reference/7.0/search-request-scroll.html#sliced-scroll
+// for details.
+type SliceQuery struct {
+	field string
+	id    *int
+	max   *int
+}
+
+// NewSliceQuery creates a new SliceQuery.
+func NewSliceQuery() *SliceQuery {
+	return &SliceQuery{}
+}
+
+// Field is the name of the field to slice against (_uid by default).
+func (s *SliceQuery) Field(field string) *SliceQuery {
+	s.field = field
+	return s
+}
+
+// Id is the id of the slice.
+func (s *SliceQuery) Id(id int) *SliceQuery {
+	s.id = &id
+	return s
+}
+
+// Max is the maximum number of slices.
+func (s *SliceQuery) Max(max int) *SliceQuery {
+	s.max = &max
+	return s
+}
+
+// Source returns the JSON body.
+func (s *SliceQuery) Source() (interface{}, error) {
+	m := make(map[string]interface{})
+	if s.field != "" {
+		m["field"] = s.field
+	}
+	if s.id != nil {
+		m["id"] = *s.id
+	}
+	if s.max != nil {
+		m["max"] = *s.max
+	}
+	return m, nil
+}