Extending report template Entity in multitenant evn

Hi
I have used the multitenant add-on in one of my projects where I can not upload Report template as it is only accessible by the Admin. Therefore, I wanted to extend the template Entity to ExtTemplate like I have extended some other Entities like Report, ReportGroup ext. However, the report_template file is not available to extend in the studio as you can see in the following image where only two other Entities under report is available, not the template.

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Thanks for your suggestions.