fix(Collaboration): Deduplicate email shares if remote share with same label exists

[provokateurin]

Summary

The current logic only deduplicates based on the uuid. This doesn't work in all scenarios, so just deduplicate by the label which would be the email or federated cloud ID.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)