[MM-47542] Extend Plugin API (#21446)

* Extend Plugin API

* Use Error, NoError in tests

* Address suggestions

* Simplify code

* Add new line

* Add featureflag and GetCollectionMetadataByIds hook

* Add enter at the end of file

* make build-templates

* Fix test

* Fix GetCollectionMetadataByIds ret type

* Add GetTopicMetadataByIds hook

* Add log

* Extract i18n

* Add experimental notice on hooks

* Update model/feature_flags.go

* Swap user to userId

* Change userId to userID

Co-authored-by: Jesse Hallam <jesse.hallam@gmail.com>

model/collection.go

@@ -0,0 +1,20 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package model
+
+type CollectionMetadata struct {
+	Id             string `json:"id"`
+	TeamId         string `json:"team_id"`
+	CollectionType string `json:"collection_type"`
+	Name           string `json:"name"`
+	RelativeURL    string `json:"relative_url"`
+}
+
+type TopicMetadata struct {
+	Id             string `json:"id"`
+	TeamId         string `json:"team_id"`
+	TopicType      string `json:"topic_type"`
+	CollectionType string `json:"collection_type"`
+	CollectionId   string `json:"collection_id"`
+}