Add disclaimer for extensions published by priviledged users

[filiptronicek]

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Following #484, it would be nice to let users know that an extension they are looking at is verified because it is published by a privileged user.

I was thinking of something like this:

If you hover on the information icon, there would be a small popup with some text. Here are some of the texts I have considered:

• This extension was published automatically. Learn more. (Learn more would lead to the publish-extensions docs). The issue with this one is that it basically only applies to @open-vsx - but there it would be useful to have.
• This extension was published by Open VSX - with some docs as well, but maybe it can be confusing.