Performance improvements for 40M posts (#7708)

* Optimizing get root posts SQL query

* Setting session invalidation to be reliable

* Adding app reciever to SessionHasPermissionToUser

* Adding app reciever to SessionHasPermissionToTeam

* Adding app reciever to SessionHasPermissionTo

* Clear session cache if permission was denied

* Fixing rebase issues

* Revert "Optimizing get root posts SQL query"

This reverts commit f364757e7015cfb4ec673d0a4fc3d57cd25d8dd7.

* Fixing build

api4/context.go

@@ -240,7 +240,7 @@ func (c *Context) LogDebug(err *model.AppError) {
 }
 
 func (c *Context) IsSystemAdmin() bool {
-	return app.SessionHasPermissionTo(c.Session, model.PERMISSION_MANAGE_SYSTEM)
+	return c.App.SessionHasPermissionTo(c.Session, model.PERMISSION_MANAGE_SYSTEM)
 }
 
 func (c *Context) SessionRequired() {