Render placeholder Tanuki image in `Maintained by` sidebars for team members without photos in `team.yml`
Background
GitLab team members who choose not to have an avatar/profile photo listed in their team.yml
entry show as broken images in the Maintained by
sidebar.
Broken image screenshot
Proposal
If no image is found in a team member's team.yml
entry, perhaps we should show a Tanuki placeholder (as used on the GitLab Team page). Other ideas welcome.