All links/versions of `initial.data` external VOEvent file point to original file

Description of problem

Currently all links of the VOEvent files initial.data point to the original file, regardless of which file or log being referenced

From: https://gracedb.ligo.org/events/E406825/files/

This prevents us from checking and downloading any of the files, except for the first one.

Expected behavior

We expect these to be versioned properly as all other files are

Steps to reproduce

Upload external event via create_event and then append using replace_event.

Context/environment

All instances of gracedb/gwcelery

Suggested solutions

Keep track of versions and fix links to use the correct version.