Set the auth session cookie to expire at the same time the session will expire

[mgwalker]

This pull request changes...

• Sets the cookie's maxAge equal to the session lifetime, which results in it getting an expiration. Verified by checking the cookie in the browser dev tools.
• closes Auth token cookie does not have an expiration #1756

This pull request is ready to merge when...

• Tests have been updated (and all tests are passing)
• This code has been reviewed by someone other than the original author
• Changelog is updated as appropriate

[cms-eapd-bot]

This deploy was cleaned up.

[codecov-io]

Codecov Report

Merging #1776 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1776      +/-   ##
==========================================
+ Coverage   93.18%   93.19%   +<.01%     
==========================================
  Files         196      196              
  Lines        4258     4259       +1     
  Branches      559      559              
==========================================
+ Hits         3968     3969       +1     
  Misses        275      275              
  Partials       15       15

Impacted Files	Coverage Δ
api/auth/session.js	100% <100%> (ø)	⬆️

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