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.

store/store.go

@@ -165,6 +165,7 @@ type PostStore interface {
 	InvalidateLastPostTimeCache(channelId string)
 	GetPostsCreatedAt(channelId string, time int64) StoreChannel
 	Overwrite(post *model.Post) StoreChannel
+	GetPostsByIds(postIds []string) StoreChannel
 }
 
 type UserStore interface {