Fix documentation link to bulk import devices

[johanstokking]

Summary

References TheThingsIndustries/lorawan-stack-docs#1227

Changes

Fix link to adding devices in bulk documentation page.

Testing

1. Go to an application
2. Click import end devices
3. Click the documentation link
4. It should not 404

Regressions

N/A

Notes for Reviewers

With the aforementioned documentation PR merged, there's no more 404, but the Console should use the right page to avoid unnecessary redirects.

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.