Add contactTags field for non-chair.

[Cryptosaurus]

The "Fetch recent coauthors" function seems to be broken (it didn't work for me as a pc member fot tosc2022_2).

As far as I can tell, the issue is at

hotcrp/iacr/collaborators.inc

Line 22 in 541762e

let tags = document.getElementsByName('contactTags')[0].value.split(' ');

This line assumes that there is an input field named contactTags, but this is only the case for chairs. This patch adds the field for all users, and should fix the "Fetch recent coauthors" function.

Note: I haven't tested the patch, and I don't know PHP, so there might be a stupid mistake in the patch :-)