Mono repo -> Master (#22553)

Combines the following repositories into one:

https://github.com/mattermost/mattermost-server
https://github.com/mattermost/mattermost-webapp
https://github.com/mattermost/focalboard
https://github.com/mattermost/mattermost-plugin-playbooks

server/channels/app/platform/link_cache.go

@@ -0,0 +1,25 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package platform
+
+import (
+	"time"
+
+	"github.com/mattermost/mattermost-server/v6/server/platform/services/cache"
+)
+
+const LinkCacheSize = 10000
+const LinkCacheDuration = 1 * time.Hour
+
+var linkCache = cache.NewLRU(cache.LRUOptions{
+	Size: LinkCacheSize,
+})
+
+func PurgeLinkCache() {
+	linkCache.Purge()
+}
+
+func LinkCache() cache.Cache {
+	return linkCache
+}