Add support for custom CA certificates

[MarkKharitonov]

I followed the instructions in https://learn.microsoft.com/en-us/windows/wsl/tutorials/wsl-containers, but the dev-containers failed to run to completion. The root cause is this command in the generated Dockerfile:

nvm install ${NODE_VERSION}

(when NODE_VERSION is not "none")
The nvm install was unable to find any versions, because our corporate network requires two custom CA certificates (ZScaler and DigiCert). The only way I could make it work is by following these steps:

1. Copy the custom certificates file (let us name it xyz.crt) to the helloworld-django directory.
2. Modify the auto generated Dockerfile:

FROM mcr.microsoft.com/vscode/devcontainers/python:0-${VARIANT}

COPY xyz.crt /xyz.crt         # !!! THIS IS THE FIRST CHANGE 

# [Choice] Node.js version: none, lts/*, 16, 14, 12, 10
ARG NODE_VERSION="none"
# !!! THIS IS THE SECOND CHANGE - notice CURL_CA_BUNDLE=/xyz.crt before calling nvm install
RUN if [ "${NODE_VERSION}" != "none" ]; then su vscode -c "umask 0002 && . /usr/local/share/nvm/nvm.sh && CURL_CA_BUNDLE=/xyz.crt nvm install ${NODE_VERSION} 2>&1"; fi

I propose to add a question asking for the path of the optional custom certificates file, so that if given it would modify the generated Dockerfile accordingly.

Relates to: <Codespaces | Remote - Containers | Both>

[chrmarti]

Continuing in #6092. Thanks.