Support grayscale feature for non-properties namespaces

[nobodyiam]

Is your feature request related to a problem? Please describe.
Currently, apollo supports the grayscale feature for properties namespaces.

However, it's not available for non-properties namespaces, e.g. xml/yml, which is strongly required by many users, see #2927.

Describe the solution you'd like
Support grayscale feature for non-properties namespaces, to make it easier, we may only support grayscale the whole text instead of some keys.

[derecknowayback]

I am interested in this issue.

[nobodyiam]

Thank you for your interest in this feature. If you are a student, you can apply for the feature on the summer-ospp website.

[SunnyBoy-WYH]

interest it.

[ywy-github]

我通过修改前端页面使得非properties格式的命名空间具有了灰度和同步的按钮，测试发现目前是可以支持非properties格式的命名空间整体进行灰度和同步的，那么目前的项目需求是支持key级别的灰度和同步吗？

[nobodyiam]

那么目前的项目需求是支持key级别的灰度和同步吗？

从实现成本考虑，可以实现为 namespace 级别的灰度和同步。
如果可能的话，对 yaml/yml 格式可以看看是否能实现 key 级别的灰度和同步。

[hezhaoye]

请教下，这个特性目前有人已经在开发了吗

[nobodyiam]

目前开源之夏还在报名阶段，我觉得应该还没有人开始开发 cc @klboke

[hezhaoye]

请教下，目前有人进入开发了吗

[klboke]

https://github.com/ywy-github 在开发中了