legacy sftp feeds on data feeds do not show keys for download.

Issue in ./help/exporting/data-feeds/download-the-data-feed-authentication-key.md

When I try to add an SFTP destination, it's supposed to show me links to download the public keys. However, the links are not actually displayed. This means that you can't actually configure an SFTP destination, as the key is mandatory.

Open help/exporting/data-feeds/download-the-data-feed-authentication-key.md and check the SFTP destination instructions where the public-key download links should appear. Confirm the links are absent, restore the documented links, and verify that the instructions show the keys needed to configure an SFTP destination.

Written by the indexing model from the issue text.