Use Gateway Stats Batch API in the Console

[PavelJankoski]

Summary

Closes #5635

Changes

When fetching gateways we were sending a request for every gateway. Now we send only one request for the loaded gateways.

Testing

1. Login in the console.
2. Go to /console/gateways page.
3. Check if the gateways have the correct status.
4. Check in developers console in Network tab if we are sending only one request related to the stats.

Notes for Reviewers

In the gateway details page we are still using the old endpoint but we are sending one request anyway. That's the reason I didn't consider changing it.

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.
• The steps/process to test this feature are clearly explained including testing for regressions.
• 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.

[kschiffer]

LGTM