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/retry.go

@@ -0,0 +1,56 @@
+// 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.
+
+// This file is based on code (c) 2014 Cenk Altı and governed by the MIT license.
+// See https://github.com/cenkalti/backoff for original source.
+
+package elastic
+
+import "time"
+
+// An Operation is executing by Retry() or RetryNotify().
+// The operation will be retried using a backoff policy if it returns an error.
+type Operation func() error
+
+// Notify is a notify-on-error function. It receives error returned
+// from an operation.
+//
+// Notice that if the backoff policy stated to stop retrying,
+// the notify function isn't called.
+type Notify func(error)
+
+// Retry the function f until it does not return error or BackOff stops.
+// f is guaranteed to be run at least once.
+// It is the caller's responsibility to reset b after Retry returns.
+//
+// Retry sleeps the goroutine for the duration returned by BackOff after a
+// failed operation returns.
+func Retry(o Operation, b Backoff) error { return RetryNotify(o, b, nil) }
+
+// RetryNotify calls notify function with the error and wait duration
+// for each failed attempt before sleep.
+func RetryNotify(operation Operation, b Backoff, notify Notify) error {
+	var err error
+	var wait time.Duration
+	var retry bool
+	var n int
+
+	for {
+		if err = operation(); err == nil {
+			return nil
+		}
+
+		n++
+		wait, retry = b.Next(n)
+		if !retry {
+			return err
+		}
+
+		if notify != nil {
+			notify(err)
+		}
+
+		time.Sleep(wait)
+	}
+}