Debian packages missing nodejs alternative

Previous versions of the Debian nodejs packages contained a postinst script which called update-alternatives to set up /usr/bin/nodejs, but recent versions no longer do this. As a result, scripts that depended on /usr/bin/nodejs being present no longer function on newly built machines, while they do still work on machines that upgraded nodejs package from a version with that script.

I've spot checked a few:

• nodejs_12.18.1-1nodesource1_amd64.deb does call update-alternatives
• nodejs_12.22.6-1nodesource1_amd64.deb does not
• nodejs_14.5.0-1nodesource1_amd64.deb does call update-alternatives
• nodejs_14.17.6-deb-1nodesource1_amd64.deb does not

(I checked by downloading the .deb file, running ar x ${file} to extract it, extracting the control file with tar -xf control.tar.*, and examining postinst if present.)

This is closely related to #1095, which is asking about Ubuntu packages, but I'm not sure if packages for Debian are distinct.

As a workaround, users can manually run the command that used to be in postinst:

update-alternatives --quiet --install /usr/bin/nodejs nodejs \
    /usr/bin/node 50 \
    --slave /usr/share/man/man1/nodejs.1.gz nodejs.1.gz \
    /usr/share/man/man1/node.1.gz