refactor(gate): add err msg for missing env vars

[destifo]

Migration notes

...

• The change comes with new or modified tests
• Hard-to-understand functions have explanatory comments
• End-user documentation is updated to reflect the change

[codecov]

Codecov Report

Attention: Patch coverage is 93.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 75.84%. Comparing base (6706680) to head (d473a06).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/typegate/src/config/types.ts	93.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #827      +/-   ##
==========================================
+ Coverage   75.75%   75.84%   +0.08%     
==========================================
  Files         144      144              
  Lines       16715    16715              
  Branches     1637     1640       +3     
==========================================
+ Hits        12663    12677      +14     
+ Misses       4029     4015      -14     
  Partials       23       23              

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[michael-0acf4]

Nice