letting organizations that block dl.boxcloud.com use the vox v

**Environment:** JS
- Preview version: 2.82 (latest)

**Steps to reproduce the problem:**
1. use a reverse proxy and instead of using api.box.com use a custom domain.
2. change the relevant constants in constants.js and build the box preview library
3. serve the build from cdn

**What is the expected behavior? (Screenshots can be helpful here)**
the expected behavior is for users from different organization to be able to view files via the box viewer and using box as storage provider. (even organizations that block the box cloud for some networking security reasons - allow them to view box content via a reverse proxy)

**What went wrong? (Screenshots, console logs, or HAR files can be helpful here)**
a request to dl.boxcloud.com happens regardless of changing all constants like API_HOST.
Is it possible that instead of a request to dl.boxcloud.com there will be a request to a reverse proxy ?

is there a documentation page that is meant as a tutorial for organizations that want to use Box Preview but use their custom domain and serve the way they want to serve it and use a reverse proxy, etc ...

Start by tracing the requests made by the built preview library after the relevant constants in constants.js, with particular attention to the dl.boxcloud.com request that remains after changing API_HOST. Reproduce the reverse-proxy build and CDN setup, then verify that Box content can load without a direct dl.boxcloud.com request when the custom domain is configured.

Written by the indexing model from the issue text.