Uploaded images 404 when using Forem in production mode

[scottnuma]

Describe the bug

Images uploaded while writing an article are 404ing when using Forem in production mode with cloudinary.

To Reproduce

I'm running quay.io/forem/forem:production with RAILS_ENV=production and RAILS_SERVE_STATIC_FILES=1 with cloudinary enabled by setting CLOUDINARY_API_KEY, CLOUDINARY_API_SECRET, and CLOUDINARY_CLOUD_NAME.

1. Click Write a post
2. Click Upload image and upload an image
3. Click to copy the markdown snippet and paste into the article to see the full link
   ![Alt Text](https://example-forem.com/localimages/uploads/articles/dv2nxpni6jb24p4ce8ij.jpg)
4. Open the pasted URL in a new tab to see a 404 page

Expected behavior

Local images show with 200 response instead of 404.

Screenshots

Desktop (please complete the following information):

• OS, version: macOS 11.2.3
• Browser, version: Version 89.0.4389.114 (Official Build) (x86_64)

Smartphone (please complete the following information):

• Device:
• OS, version:
• Browser, version:

Additional context

The upload button copies the following to my clipboard:

![Alt Text](https://example-forem.com/localimages/uploads/articles/dv2nxpni6jb24p4ce8ij.jpg)

If I edit the URL to remove /localimages, the image loads successfully. Looking at the file directory, I can see that /opt/apps/forem/public/uploads/ contains the images I've uploaded. I can also see that there is no localimages directory in public.

Searching through the codebase for localimages, it looks like the image URL is prefixed with /localimages due to the Carrierwave config in carrierwave.rb.

Is this config to allow a reverse proxy to serve /localimages requests? I think it would be useful to have the config.asset_host suffix be configurable by environment variable, and defaulting to /localimages if that's the usual method for production deployments. I can open a pull request if that's helpful.

As a workaround without altering the source code / image, I've found that adding a symlink for /opt/apps/forem/public/localimages/uploads fixes the generated URL.

mkdir /opt/apps/forem/public/localimages
ln -s /opt/apps/forem/public/uploads/ /opt/apps/forem/public/localimages/uploads

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