Give a warning before trying to publish symbols-only packages

[aholstrup1]

❔What, Why & How

We've seen a couple of issues where builds are failing because one of the installApps is a symbols-only package. We could improve a bit here by displaying a warning when people try to do this. Eventually, this should probably be an error but showing a warning is a good first step IMO.

Related to issue: #1512

✅ Checklist

• [x] Add tests (E2E, unit tests)
• [x] Update RELEASENOTES.md
• [x] Update documentation (e.g. for new settings or scenarios)