Enable admin to search by email

[ethantkoenig]

Allow admins to search for users by email.

[codecov-io]

Codecov Report

Merging #2888 into master will decrease coverage by <.01%.
The diff coverage is 50%.

@@            Coverage Diff            @@
##           master   #2888      +/-   ##
=========================================
- Coverage    26.8%   26.8%   -0.01%     
=========================================
  Files          90      90              
  Lines       17807   17810       +3     
=========================================
  Hits         4774    4774              
- Misses      12353   12355       +2     
- Partials      680     681       +1

Impacted Files	Coverage Δ
models/user.go	21.87% <50%> (-0.08%)	⬇️

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[lunny]

LGTM

[lafriks]

LGTM