User Data registration via UI doesn't honour the domain field

##### ISSUE TYPE

* Bug Report

##### COMPONENT NAME

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User Data
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##### CLOUDSTACK VERSION

4.19 (would be present from 4.18 - when managed user data service support was added)
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##### CONFIGURATION

##### OS / ENVIRONMENT

##### SUMMARY

Registration of user data in a specific domain i.e., by passing the domain in the UI , doesn't honour the domain id passed, rather creates the user data in the domain you are currently logged in to.

##### STEPS TO REPRODUCE

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1. Log in as Admin
2. Create a domain - domain1 under ROOT domain
3. As Admin in the ROOT domain context, register a user data and pass domain as /domain1
4. User data is registered but the domain appears as ROOT and not /domain1
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##### EXPECTED RESULTS

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User data be registered in the correct domain
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##### ACTUAL RESULTS

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User data created / registered in the domain in the current context
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首先在 UI 中复现 User Data 注册流程：在 ROOT 下创建 domain1，然后从 ROOT 上下文注册 User Data，同时传入 /domain1。跟踪 UI 中的注册入口以及 domain 字段的处理方式。当 User Data 被创建在 domain1 中而不是当前的 ROOT 域中时，即表示完成。

由索引模型根据 Issue 内容生成。