[FIX:] azurerm_cdn_frontdoor_custom_domain - allow wildcard host_name with ManagedCertificate

[WodansSon]

What does this PR do?

This PR removes the provider-side validation that rejected wildcard host_name values when tls.certificate_type is ManagedCertificate.

Azure Front Door now supports managed certificates for wildcard custom domains, so the existing validation was blocking a valid configuration at plan time.

Changes in this PR

• remove the wildcard ManagedCertificate rejection from custom domain validation
• keep the existing 64-character host_name limit for ManagedCertificate
• update acceptance coverage to keep the negative long-hostname case and add a positive wildcard managed-certificate case
• update the resource documentation to reflect that wildcard managed certificates are supported

Why is this needed?

Before this change, a configuration such as a wildcard custom domain with:

tls {
  certificate_type = "ManagedCertificate"
}

Related Issue(s)

Fixes #32730