maintainer-list: Fix missing githubId's

All these IDs were carefully obtained with
- If possible, look at which commit introduced the maintainer and check
  with the GitHub API whether it was the person we think it should be.
  If yes, that's great
- If above doesn't work for any reason (which was the case for about
  half), then I went through the commit log and through GitHub PRs
  manually, to see who the person is

Sometimes this required trying to find a commit after the svn-era, but
before the committer stopped contributing. Sometimes when one person
adds two maintainers this required checking that they are known to each
other through bidirectional GitHub follows.

For tweber's github, see:
https://github.com/NixOS/nixpkgs/pull/82461#issuecomment-599433112