Add smoke tests for entity subpages

[kschiffer]

Summary

OS counterpart of https://github.com/TheThingsIndustries/lorawan-stack/pull/3382

Changes

• Add smoke tests for application subpages
• Add smoke tests for gateway subpages
• Add smoke tests for organization subpages

Notes for Reviewers

See https://github.com/TheThingsIndustries/lorawan-stack/pull/3382

This depends on https://github.com/TheThingsNetwork/lorawan-stack/pull/5693 to be merged

Checklist

• [x] Scope: The referenced issue is addressed, there are no unrelated changes.
• [x] 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.
• [x] Documentation: Relevant documentation is added or updated.
• [x] Changelog: Significant features, behavior changes, deprecations and fixes are added to CHANGELOG.md.
• [x] Commits: Commit messages follow guidelines in CONTRIBUTING.md, there are no fixup commits left.