docs(test): clarify docker usage for windows (#29274)

Team members on Windows were having trouble running tests inside of
Docker. Given that headed tests must use WSL, I think it makes sense to
have Windows devs use WSL for any E2E tests run inside of Docker. That
way they aren't switching back and forth between shells.

This PR clarifies the Docker docs that instruct devs on how to use WSL.

Author: liamdebeasi