Fix request to /staticfiles failing during dev

[Arnei]

Fixes #1023.

The created request to /staticfiles were not matching our proxy regex. This fixes that.

How to test this

This only affects development, not completed builds, so you will have to install this PR yourself and run it locally. You will also need an Opencasts with themes enabled that you can proxy against. Then open the "Create Theme" dialog and check if you can successfully upload a file in any of the file uploads.

[github-actions]

This pull request is deployed at test.admin-interface.opencast.org/1024/2024-12-20_08-30-33/ .
It might take a few minutes for it to become available.

[github-actions]

Use docker or podman to test this pull request locally.

Run test server using develop.opencast.org as backend:

podman run --rm -it -p 127.0.0.1:3000:3000 ghcr.io/opencast/opencast-admin-interface:pr-1024

Specify a different backend like stable.opencast.org:

podman run --rm -it -p 127.0.0.1:3000:3000 -e PROXY_TARGET=https://stable.opencast.org ghcr.io/opencast/opencast-admin-interface:pr-1024

It may take a few seconds for the interface to spin up.
It will then be available at http://127.0.0.1:3000.
For more options you can pass on to the proxy, take a look at the README.md.