Add API token to UserSerializer

Codecov Report

Merging #135 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #135   +/-   ##
=======================================
  Coverage   71.04%   71.04%           
=======================================
  Files         176      176           
  Lines        7588     7588           
=======================================
  Hits         5391     5391           
  Misses       2197     2197

Impacted Files	Coverage Δ
arkindex/users/serializers.py	100% <ø> (ø)

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merged

mentioned in commit 92fd2de1