Out-of-the-box, WordPress provides the ability to blacklist comments or configure a set of options to send comments to moderation. If all comments are moderated, there are no options to whitelist comments.
Searching the plugin directory for comment whitelisting provides few, if any, solutions. However, a cursory search of Google led me to the Comment Whitelist plugin by Alejandro Carravedo.
Comment Whitelist adds a ‘Put in Whitelist’ quick moderation link to comments that makes adding email addresses to the list an easy task. One thing to keep in mind is that the whitelist uses email addresses and it’s possible comments from people impersonating whitelisted users may get published.
Despite not being updated in more than nine years, the plugin works as advertised. You’ll need to download the zip file and manually install it as you won’t be able to find it by searching the plugin directory from the WordPress backend.
WP-SpamShield allows me to add IPs or emails to a whitelist that I can enable, though I’ve never used the functionality before. Figured I’d mention it as it’s a good (and up to date) alternative to the plugin you found.