[Feature Request] Allow updating the base URL for reverse proxies

[origintopleft]

slack-export-viewer is containerized with a very bare bones Dockerfile, mentioned primarily for completeness:

FROM python:3.11
RUN pip install slack-export-viewer
ENTRYPOINT [ "python3", "/usr/local/bin/slack-export-viewer" ]

I'm trying to run several slack-export-viewers on the same host, and I'm trying to put them all on NGINX reverse proxy at URLs like /workspace1, /workspace2... but because the export viewer itself assumes it will always be serving from /, I just get a lot of unstyled links and HTTP 404 errors in the browser tools.

(This particular deployment is going only to myself and two other people, so we can fall back to port numbers for now, but I'd like to submit a feature request anyway since I didn't see anything to 👍 vote already.)