PLT-6472: Basic Elastic Search implementation. (#6382)

* PLT-6472: Basic Elastic Search implementation.

This currently supports indexing of posts at create/update/delete time.
It does not support batch indexing or reindexing, and does not support
any entities other than posts yet. The purpose is to more-or-less
replicate the existing full-text search feature but with some of the
immediate benefits of using elastic search.

* Alter settings for AWS compatability.

* Remove unneeded i18n strings.

einterfaces/elasticsearch.go

@@ -0,0 +1,23 @@
+// Copyright (c) 2017-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package einterfaces
+
+import "github.com/mattermost/platform/model"
+
+type ElasticSearchInterface interface {
+	Start() *model.AppError
+	IndexPost(post *model.Post, teamId string)
+	SearchPosts(channels *model.ChannelList, searchParams []*model.SearchParams) ([]string, *model.AppError)
+	DeletePost(postId string)
+}
+
+var theElasticSearchInterface ElasticSearchInterface
+
+func RegisterElasticSearchInterface(newInterface ElasticSearchInterface) {
+	theElasticSearchInterface = newInterface
+}
+
+func GetElasticSearchInterface() ElasticSearchInterface {
+	return theElasticSearchInterface
+}