Adds direct participants to the channel invite (#30404)

* Adds direct participants to the channel invite

The channel invite now contains the sanitized users that are local to
the node that is sending the invite. In the event that the receiving
server doesn't have those users in its local database, it can create
them from the invite and correctly generate the DM or GM with them as
members.

* Use IsRemote instead of directly checking user attributes

---------

Co-authored-by: Miguel de la Cruz <miguel@ctrlz.es>
Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/app/platform/shared_channel_notifier.go

@@ -145,7 +145,7 @@ func handleInvitation(ps *PlatformService, syncService SharedChannelServiceIFace
 		return errors.Wrap(err, fmt.Sprintf("couldn't find remote cluster %s, for creating shared channel invitation for a DM", *participant.RemoteId))
 	}
 
-	return syncService.SendChannelInvite(channel, creator.Id, rc, sharedchannel.WithDirectParticipantID(creator.Id), sharedchannel.WithDirectParticipantID(participant.Id))
+	return syncService.SendChannelInvite(channel, creator.Id, rc, sharedchannel.WithDirectParticipant(creator), sharedchannel.WithDirectParticipant(participant))
 }
 
 func getUserFromEvent(ps *PlatformService, event *model.WebSocketEvent, key string) (*model.User, error) {