Add ctags binary path to zoekt-indexserver

Created by: camdencheek

Running sg start was failing for me because zoekt-indexserver could not find the ctags binary. This is ostensibly because I don't have either universal ctags or exuberant ctags installed, but it looks like elsewhere, we use cmd/symbols/universal-ctags-dev, so I copied that same pattern here.

Fixes #19882 (closed)