template visibility in subdomains

##### ISSUE TYPE
* Improvement Request

##### COMPONENT NAME

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UI
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##### CLOUDSTACK VERSION

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4.19.0.0
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##### SUMMARY

We are a school and use domains for different groups of classes. It would be good if there was an option for public templates/ISOs to be visible in subdomains as well.
We cannot find a way to display templates/ISOs in the parent domain and in the subdomains. With the setting share.public.templates.with.other.domains we can share templates with all domains or only with the current domain. However, there is no way to share the template only in the parent domain and in the subdomain. This would be a good extension function. With shared networks, for example, this is possible. With a parameter such as share.public.templates.with.sub.domains this could be achieved.
For example:
share.public.templates.with.other.domains=false
share.public.templates.with.sub.domains=true

先追蹤 share.public.templates.with.other.domains 設定和 template/ISO 可見性的處理方式，然後將其與 shared-network 的行為進行比較。當父網域可以向其子網域公開 template 和 ISO，而不會將它們公開給每個網域，且要求的設定已完成文件化並由測試涵蓋時，即表示完成。

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