Switch back to $proxy_host

[bjester]

Summary

Description of the change(s) you made

• Switch content reverse proxy back to using Host: $proxy_host as GCS does not like it if it's different

References

Fixes regression from #4564

Comments

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Contributor's Checklist

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Reviewer's Checklist

This section is for reviewers to fill out.

• Automated test coverage is satisfactory
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• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
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