Is your feature request related to a problem? Please describe.
We currently have an approved extension (pxt-micrbit-ml), which to be useful needs additional files to be injected by a different environment that embeds MakeCode.
So, this extension doesn’t offer any usable functionality on its own, and doesn't make much sense for a normal MakeCode user to add it to their project.

Describe the solution you'd like
It would be useful to have something like a flag in pxt.json file, to be able to hide an extension from the search.

Describe alternatives you've considered
There is already a hidden key in PackageConfig, but it must have a different purpose as it didn't work in our tests.
https://github.com/microsoft/pxt/blob/v11.3.1/localtypings/pxtpackage.d.ts#L82

We also tried removing the for PXT/microbit metadata from the extension README file, but that didn't work either.

In this case the extension needs to be approved, as it contain an editor extension as well, so removing it from the approval list would not be an option.

Additional context
N/A