azurerm_cdn_endpoint - fix API error when given an empty origin_host_header

[magodo]

Confirmed with service team, the request payload can't contain an empty string for the origin_host_header, otherwise, the service will raise following error:

{
  "error": {
    "code": "BadRequest",
    "message": "OriginHostHeader \"\" is invalid. It must be a valid domain name, IP version 4, or IP version 6."
  }
}

Also update the document of this property to remove the line about default, since that is not true.

Meanwhile, this should fix some of the acctest failures.

Fixes #8870, #11107.

[katbyte]

LGTM 👍

[ghost]

This has been released in version 2.61.0 of the provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading. As an example:

provider "azurerm" {
    version = "~> 2.61.0"
}
# ... other configuration ...

[github-actions]

I'm going to lock this pull request because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active contributions.
If you have found a problem that seems related to this change, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.