bugfix: MockGenericConfigService - set timestamps in response

[GurtejSohi]

In the PR for exposing creation and update timestamp in UpsertConfigResponse, I missed setting the timestamps in UpsertConfigResponse in MockGenericConfigService. This change fixes it.

[codecov]

Codecov Report

Merging #30 (88b2813) into main (d8d541a) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##               main      #30   +/-   ##
=========================================
  Coverage     90.50%   90.50%           
  Complexity      109      109           
=========================================
  Files            14       14           
  Lines           400      400           
  Branches         18       18           
=========================================
  Hits            362      362           
  Misses           32       32           
  Partials          6        6           

Flag	Coverage Δ	Complexity Δ
integration	90.50% <ø> (ø)	0.00 <ø> (ø)
unit	88.38% <ø> (ø)	0.00 <ø> (ø)

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[github-actions]

Unit Test Results

10 files  ±0  10 suites  ±0   6s ⏱️ -1s
31 tests ±0  31 ✔️ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit 69a7275. ± Comparison against base commit d8d541a.