Omit empty deployment context fields (#2903)

[sjberman]

Problem: If an optional deployment context field wasn't set, an empty value would still be sent and cause the reporting server to return a 400.

Solution: Use pointers on the optional fields to omit them from the context if they're empty.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.71%. Comparing base (e153640) to head (616f397).
Report is 1 commits behind head on release-1.5.

Additional details and impacted files

@@             Coverage Diff              @@
##           release-1.5    #2910   +/-   ##
============================================
  Coverage        89.71%   89.71%           
============================================
  Files              109      109           
  Lines            11091    11091           
  Branches            50       50           
============================================
  Hits              9950     9950           
  Misses            1082     1082           
  Partials            59       59           

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