Create mfe_config to frontend-base conversion endpoint

### Description

Create a new sister endpoint to mfe_config that reads any existing configuration data (currently django settings or site configuration) and outputs it in the format expected by frontend-base.  See https://github.com/openedx/frontend-base/issues/118.

### PRs

- https://github.com/openedx/frontend-base/pull/179
- https://github.com/openedx/openedx-platform/pull/38061