Fix cannot remove all attributes in general settings

[PavelJankoski]

Summary

References #7466

Changes

• Change the attributes validation to also check empty object.

Testing

Steps

Check if you are gonna be able to remove all the attributes and then click "Save changes".

Results

Changes should be saved successfully and after refreshing the page, the attributes should not be there.

Notes for Reviewers

Beside the device general settings, this was also not working for the gateways and applications, because they all are using the same validation function.

Checklist

• Scope: The referenced issue is addressed, there are no unrelated changes.
• Compatibility: The changes are backwards compatible with existing API, storage, configuration and CLI, according to the compatibility commitments in README.md for the chosen target branch.
• Documentation: Relevant documentation is added or updated.
• Testing: The steps/process to test this feature are clearly explained including testing for regressions.
• Infrastructure: If infrastructural changes (e.g., new RPC, configuration) are needed, a separate issue is created in the infrastructural repositories.
• 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.