Add option to publish to different providers under different circumstances.

[ariporad]

Hi,

I'd like to be able to have electron-builder publish to different providers under different circumstances. For example, publishing to github onTagOrDraft, but publishing to S3 only on a tag.

I really like the workflow of having draft releases with always up-to-date build artifacts, but I don't want WIP releases to get uploaded to S3 (where the actual auto-updater is fed from).

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.