MM-56876: Redis: first introduction (#27752)

```release-note
NONE
```

---------

Co-authored-by: Jesús Espino <jespinog@gmail.com>
Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/app/post.go

@@ -118,7 +118,7 @@ func (a *App) deduplicateCreatePost(rctx request.CTX, post *model.Post) (foundPo
 	}
 
 	if nErr != nil {
-		return nil, model.NewAppError("errorGetPostId", "api.post.error_get_post_id.pending", nil, "", http.StatusInternalServerError)
+		return nil, model.NewAppError("errorGetPostId", "api.post.error_get_post_id.pending", nil, "", http.StatusInternalServerError).Wrap(nErr)
 	}
 
 	// If another thread saved the cache record, but hasn't yet updated it with the actual post