MM-42810: Using websocket broadcast hook for permalink preview (#28627)

We use the newly introduced websocket broadcast hook system
to implement permalink preview efficiently. This is essentially
a re-do of https://github.com/mattermost/mattermost/pull/23812
using the new system.

https://mattermost.atlassian.net/browse/MM-42810
```release-note
NONE
```

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/app/platform/web_hub.go

@@ -24,6 +24,7 @@ const (
 type SuiteIFace interface {
 	GetSession(token string) (*model.Session, *model.AppError)
 	RolesGrantPermission(roleNames []string, permissionId string) bool
+	HasPermissionToReadChannel(c request.CTX, userID string, channel *model.Channel) bool
 	UserCanSeeOtherUser(c request.CTX, userID string, otherUserId string) (bool, *model.AppError)
 }