fix(sudo): Selectively log user email on superuser access

[RyanSkonnord]

This can leak PII for users from orgs other than the staff org, per https://github.com/getsentry/team-core-product-foundations/issues/315

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.12%. Comparing base (fcb48c7) to head (f06ccef).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #72611      +/-   ##
==========================================
+ Coverage   78.00%   78.12%   +0.11%     
==========================================
  Files        6635     6622      -13     
  Lines      296661   295659    -1002     
  Branches    51087    50931     -156     
==========================================
- Hits       231416   230986     -430     
+ Misses      58863    58383     -480     
+ Partials     6382     6290      -92     

Files	Coverage Δ
src/sentry/conf/server.py	87.82% <100.00%> (+0.02%)	⬆️
src/sentry/middleware/superuser.py	97.36% <100.00%> (+7.36%)	⬆️

... and 943 files with indirect coverage changes

[RyanSkonnord]

Having found no good way to bind this to an actual auth provider, I've kludged in a single-purpose conf value that should do the trick. It should be pretty easy to refactor out again if anyone wants to take another pass later.