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

まず share.public.templates.with.other.domains 設定と template/ISO の可視性処理を追跡し、次に shared-network の動作と比較します。親ドメインがすべてのドメインに公開することなく、サブドメインに template と ISO を公開でき、要求された設定が文書化され、テストでカバーされていれば完了です。

索引モデルが issue の本文から書いたものです。