fix: make terraform imports keys order deterministic

[pmalek]

generateImportKeys generated terraform's import keys. The test assumes that the keys are always in the same order but they are not as they are generated using a map which does not yield the same order each time it's being looped over.

This PR fixes that by sorting the keys on each marshal operation.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 54.28571% with 16 lines in your changes missing coverage. Please review.

Project coverage is 27.55%. Comparing base (3305886) to head (f6f1880).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
kong2tf/generate_resource.go	54.28%	10 Missing and 6 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1433      +/-   ##
==========================================
+ Coverage   27.51%   27.55%   +0.03%     
==========================================
  Files          61       61              
  Lines        6272     6294      +22     
==========================================
+ Hits         1726     1734       +8     
- Misses       4423     4432       +9     
- Partials      123      128       +5     

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