"Pages to Workers" compatibility matrix is missing "Add a custom domain to a branch" feature

### Existing documentation URL(s)

- https://developers.cloudflare.com/workers/static-assets/migration-guides/migrate-from-pages/#compatibility-matrix
- https://developers.cloudflare.com/pages/how-to/custom-branch-aliases/
- https://developers.cloudflare.com/workers/configuration/previews/

### What changes are you suggesting?

Pages has the (well-documented) ability to point a custom domain to a branch, not only to the main production deployment.

Workers does not have that feature yet, as noted at the bottom of the "Preview URLs" documentation:

> You cannot currently configure Preview URLs to run on a subdomain other than workers.dev.

However, the "Preview URLs" and "Custom Subdomains" rows of the compatibility table show ✅ for Workers, even though it is missing this important feature.

This limitation needs to be added to the compatibility table.

### Additional information

We rely on custom domains for branch previews, because we need to use shared cookies. It was frustrating to spend time planning a migration from Pages to Workers, only to discover that we can't use Workers yet because it is missing this feature.