Release EUIs of deleted gateways

[bafonins]

Summary

Closes #1120

Changes

• Add afterDelete hook for gateways to reset their eui.
• Update gateway deletion modal text.

Checklist

• Scope: The referenced issue is addressed, there are no unrelated changes.
• Compatibility: The changes are backwards compatible with existing API, database and configuration, according to the stability commitments in README.md.
• Testing: The changes are covered with unit tests. The changes are tested manually as well.
• Documentation: Relevant documentation is added or updated.
• Changelog: Significant features, behavior changes, deprecations and fixes are added to CHANGELOG.md.
• Commits: Commit messages follow guidelines in CONTRIBUTING.md, there are no fixup commits left.

[coveralls]

Coverage decreased (-0.01%) to 73.371% when pulling 798fe98 on feature/1120-eui-release into 187be34 on master.

[htdvisser]

Looks good to me 👍

[t0mZ4]

Hi

I still see an issue when I use the CLI to delete a gateway, and then I cannot re-add the gateway with the same id.

error:pkg/identityserver/store:id_taken (ID already taken)
    correlation_id=fc206b725e0543d691dafa5a4d8d2674

any way to workaround this!?

[htdvisser]

The EUI was released when you deleted the gateway, but the ID is still reserved.

This is for security reasons, as historical data (in external integrations) is linked to the ID, and if someone else would register a gateway with the same ID after you delete it, they would have access to your historical data, which probably isn't what you want.

With #3467 it's possible for admin users to release the IDs, but of course that could cause some security issues like the one I described above.