Make epivis API requests more visible

[melange396]

We dont have an easy way to distinguish epivis-originated API requests in our server logs, making it somewhat difficult to measure actual usage of epivis. We could prepend/append to or replace (im not sure right now which choice would be most appropriate) the User-Agent header with something epivis specific, or we could possibly do it via the Origin or Referer headers instead.

Current headers (for me) appear to be something like:

Origin: https://delphi.cmu.edu
Referer: https://delphi.cmu.edu/
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36

[melange396]

As mentioned in cmu-delphi/delphi-epidata#1386 (comment) , we may need to update our Referrer-Policy.

[rzats]

Currently a somewhat hacky way of tracking epivis requests is looking for API requests with years 3921 - 3924 as the upper date bound: #53 (comment)

This is caused by a bug, though, and should be patched out once this issue is closed.