Add admin ability to view a registration application for a given local user.

[dessalines]

Requirements

• This is a feature request and not a bug report. Otherwise, please create a new bug report instead.
• Please check to see if this request (or a similar one) already exists.
• It's a single feature. Please don't request multiple features in one issue.

Describe the feature you'd like

As part of the person's dropdown menu, it'd be nice to be able to view their registration application, to have some context on whether to take action on a new account.

Backend PR: LemmyNet/lemmy#4913