Deprecate gemini vertex

[willbakst]

Closes #817

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (b8ec0f0) to head (9508b91).
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #819   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          485       485           
  Lines        19025     19031    +6     
=========================================
+ Hits         19025     19031    +6     

Flag	Coverage Δ
tests	100.00% <ø> (ø)

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