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

首先跟踪 share.public.templates.with.other.domains 设置以及 template/ISO 可见性的处理方式，然后将其与 shared-network 的行为进行比较。当父域可以向其子域公开 template 和 ISO，而不会将它们公开给每个域，并且所请求的配置已编写文档并由测试覆盖时，即视为完成。

由索引模型根据 Issue 内容生成。