Description of the Change

Correct the link on the Index Health page when no indexes are found.

Closes #2641.

Verification Process

1. Delete any indexes via WP CLI, wp elasticpress delete-index.
2. Visit ElasticPress > Index Health.
3. You'll see a message, "We could not find any data for your Elasticsearch indices. Maybe you need to sync your content?". Follow the "sync your content" link.
4. You should be taken to the ElasticPress > Sync page.

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.