``conan art:promote`` might not promote package metadata

[memsharded]

The current implementation does a explicit list of files to be promoted.

But there might be package-metadata files to promote, and they will not be promoted. For the export/recipe part case, it might not be an issue because the full folder is promoted.

Coming from #249 (comment)

[aagor]

Hi @memsharded,

I got an example in our company where exactly this happens.
A recipe and some packages are promoted between two Artifactory repositories, leaving behind the package metadata.

Source code says:

conan-extensions/extensions/commands/art/cmd_promote.py

Line 81 in 5155aeb

# TODO: Do we want to support metadata promotion?

Is there a reason why the metadata is not promoted?