As an alternative, until Atlassian delivers this, you can give Better Commit Policy for Bitbucket a try! It allows you to install local hooks, so you can verify commit right on the developers' computer at commit time. As long as it's consistently used across the developer team, it can work as an alternative to a server-side hook.
(Please note that the app relies on Better Commit Policy for Jira!)
Yes, that's why I mentioned local hooks, as a workaround (and that it relies on Better Commit Policy for Jira Server) until Atlassian delivers pre-receive hooks. As long as the local hooks are consistently used across the developer team, it can work as an alternative to a server-side hook.
So it's not yet available to be directly installed on Bitbucket Cloud, and Bitbucket Cloud also doesn't allow you to configure pre-receive hooks. You can read more about how this workaround can work here.