Forcing HTTPS prevents Wiki Image Uploads

I have deployed Gitlab through docker. E.g.

HOSTNAME="gitlab.mydomain.com"

docker run --detach \
    --hostname $HOSTNAME \
    --publish 443:443 --publish 80:80 \
    --publish 23825:22 \
    --name gitlab \
    --restart always \
    --volume $PWD/gitlab/config:/etc/gitlab \
    --volume $PWD/gitlab/logs:/var/log/gitlab \
    --volume $PWD/gitlab/data:/var/opt/gitlab \
    gitlab/gitlab-ce:latest

I was asked to force HTTPS so that all traffic was encrypted. I found the easiest solution for us was to just add the relevant rules to our nginx reverse proxy and update the DNS to forward all traffic through there. The proxy will pick up non HTTPS traffic and redirect it to HTTPS. It will also take that HTTPS traffic, decrypt it, and pass on a plain HTTP request to the server running Gitlab through docker.

After the changes, everything seemed to work fine, except that we noticed that we can no longer upload images to the wiki (however uploading images to the issues works just fine.). If you try to upload to the wiki (either by file, or from clipboard), then you get the following error message in the console:

It looks to me that the request is getting blocked because it is using HTTP instead of HTTPS. What should I do to resolve this (and keep SSL enabled)?