[Docker] Can't build Docker image

### Description

Building the docker image on a Windows 11 machine as described [here](https://github.com/lowRISC/opentitan/blob/master/util/container/README.md) fails due to some mistakes in the Dockerfile, of which only one (line endings of a Python not being converted from Dos to Unix format) appears to be Windows-specific.
I forked the repo and fixed the Dockerfile. I can prepare a pull request with my fixes, but I didn't include the sign-off text in each commit. Is there an easy way to fix this so that I can contribute back the fixed version?

Start with util/container/README.md and the Dockerfile used by its documented build procedure. Reproduce the image build on Windows 11, inspect the reported Dockerfile mistakes including Python script line endings, and compare the result with the reporter's fixes. Done means the documented Docker build succeeds and the contribution can be prepared with the required sign-off.

Written by the indexing model from the issue text.