fix(publisher-s3): ensure published files do not overwrite multiple arches

[MarshallOfSound]

I don't think anyone can viably be using this publisher for multiple arches at the moment without using the keyResolver which this change doesn't impact. There's a world where this breaks someone, but I don't think we make any documented guarantees around where the file gets uploaded too exactly in the bucket (maybe we should document that once this lands?)

[erickzhao]

but I don't think we make any documented guarantees around where the file gets uploaded too exactly in the bucket (maybe we should document that once this lands?)

We do document the default key structure at least. It used to only say this:

By default, all files are positioned at the following key:

${config.folder || appVersion}/${artifactName}"

But I added a whole section on using keyResolver as a workaround for the problem this PR is fixing: electron-forge/electron-forge-docs@17e01c5

[mahnunchik]

Let's deal with S3 and GCS publisher together.

Possible improvements for both:

• common StaticArtifact
• move s3KeySafe to common utils