[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>

plugin/api.go

@@ -1157,6 +1157,17 @@ type API interface {
 	//
 	// Minimum server version: 7.1
 	EnsureBotUser(bot *model.Bot) (string, error)
+
+	// RegisterCollectionAndTopic informs the server that this plugin handles
+	// the given collection and topic types.
+	//
+	// It is an error for different plugins to register the same pair of types,
+	// or even to register a new topic against another plugin's collection.
+	//
+	// EXPERIMENTAL: This API is experimental and can be changed without advance notice.
+	//
+	// Minimum server version: 7.6
+	RegisterCollectionAndTopic(collectionType, topicType string) error
 }
 
 var handshake = plugin.HandshakeConfig{