Fix ttnv3 source related bugs

[happyRip]

Summary

Ref https://github.com/TheThingsIndustries/lorawan-stack-support/issues/929

Changes

• Update End Devices ids and {created,updated}_at fields when getting the device from AS, JS and NS
  • validate that ids either match between the devices or are not present

Testing

Application https://eu1.cloud.thethings.network/console/applications/migrate-without-joineui contains a device registered without the JoinEUI that I attempted to export. The device was exported successfully.

Regressions

n/a

Notes for Reviewers

I attached other bugfix commits that otherwise would only be added in #65

Current solution only checks if the fields match and considers empty ("") fields matching any other field. This could be left for now or handled in 2 ways:

• first
  • instead of having identifiers a and b there are dst destination and src source identifiers
  • dst ids overwrite empty src ids so that the fields that would be overwritten by an empty value won't be overwritten
• second
  • some way of filtering paths so that when the src value is empty it is removed from the paths and then can be removed post-validation

Checklist

• Scope: The referenced issue is addressed, there are no unrelated changes.
• Documentation: Relevant documentation is added or updated.
• Changelog: Significant features, behavior changes, deprecations and fixes are added to CHANGELOG.md.