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_collapse_builder.go

@@ -0,0 +1,68 @@
+// 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
+
+// CollapseBuilder enables field collapsing on a search request.
+// See https://www.elastic.co/guide/en/elasticsearch/reference/7.0/search-request-collapse.html
+// for details.
+type CollapseBuilder struct {
+	field                      string
+	innerHit                   *InnerHit
+	maxConcurrentGroupRequests *int
+}
+
+// NewCollapseBuilder creates a new CollapseBuilder.
+func NewCollapseBuilder(field string) *CollapseBuilder {
+	return &CollapseBuilder{field: field}
+}
+
+// Field to collapse.
+func (b *CollapseBuilder) Field(field string) *CollapseBuilder {
+	b.field = field
+	return b
+}
+
+// InnerHit option to expand the collapsed results.
+func (b *CollapseBuilder) InnerHit(innerHit *InnerHit) *CollapseBuilder {
+	b.innerHit = innerHit
+	return b
+}
+
+// MaxConcurrentGroupRequests is the maximum number of group requests that are
+// allowed to be ran concurrently in the inner_hits phase.
+func (b *CollapseBuilder) MaxConcurrentGroupRequests(max int) *CollapseBuilder {
+	b.maxConcurrentGroupRequests = &max
+	return b
+}
+
+// Source generates the JSON serializable fragment for the CollapseBuilder.
+func (b *CollapseBuilder) Source() (interface{}, error) {
+	// {
+	//   "field": "user",
+	//   "inner_hits": {
+	//     "name": "last_tweets",
+	//     "size": 5,
+	//     "sort": [{ "date": "asc" }]
+	//   },
+	//   "max_concurrent_group_searches": 4
+	// }
+	src := map[string]interface{}{
+		"field": b.field,
+	}
+
+	if b.innerHit != nil {
+		hits, err := b.innerHit.Source()
+		if err != nil {
+			return nil, err
+		}
+		src["inner_hits"] = hits
+	}
+
+	if b.maxConcurrentGroupRequests != nil {
+		src["max_concurrent_group_searches"] = *b.maxConcurrentGroupRequests
+	}
+
+	return src, nil
+}