Geo: Design thumbnails are not replicated

Summary

Image thumbnails for design management uploads are not downloaded on a Geo secondary.

Steps to reproduce

1. On the Geo primary, create an issue.
2. On the issue's Designs tab, upload an image. A thumbnail should appear when uploading is finished.
3. View the issue on the Geo secondary. The thumbnail will show a file name, but no image is displayed

Example Project

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What is the current bug behavior?

Design thumbnails are not downloaded to the secondary.

What is the expected correct behavior?

Design thumbnails should be downloaded to the secondary and appear in an issue's Designs tab.

Relevant logs and/or screenshots

geo.log shows:

{"severity":"ERROR","time":"2020-05-20T13:43:50.448Z","correlation_id":"735db9849da24b3a8899ea3e6bc43af0","class":"Geo::FileDownloadService","host":"127.0.0.1","message":"Cannot find a handler for G        itlab::Geo Downloader for object_type = 'design_management/design_v432x230'","job_id":"2fb7bb5419c9ed902b997a41","object_type":"design_management/design_v432x230","object_db_id":2}

Screenshot of primary:

Screenshot of secondary:

Output of checks

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Results of GitLab environment info

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`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production`)

Results of GitLab application Check

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sudo gitlab-rake gitlab:check SANITIZE=true)
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sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true)
(we will only investigate if the tests are passing)

Possible fixes

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