Add third-party logos used in Trial Registration reassurance sidebar

Purpose

Migrating over a handful of third-party logos as part of the promotion of an experiment aimed at improving trial registration & creation rates which has been deemed a success.

Screenshots

Close up of the logos:

Usage in the application:

Checklist

For third-party trademarks:

• If this adds or updates an icon or illustration that includes a third-party trademark, ensure that it follows the process for adding third-party trademarks to GitLab.
  • Approval to migrate

Closes #272 (closed) & relates to gitlab#348341 (closed)