chore: Code coverage offensive #1: util/dex

[jannfis]

Code coverage offensive

This is the first part of an effort to increase our overall code coverage for tests to an acceptable limit.

The PR adds units test for util/dex package with a package coverage of 88.5%. Previous package coverage was 0% (not a single test).

Checklist:

• (c) this does not need to be in the release notes.
• The title of the PR states what changed and the related issues number (used for the release note).
• I've updated both the CLI and UI to expose my feature, or I plan to submit a second PR with them.
• Optional. My organization is added to USERS.md.
• I've signed the CLA and my build is green (troubleshooting builds).

[codecov]

Codecov Report

Merging #3305 into master will increase coverage by 0.27%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3305      +/-   ##
==========================================
+ Coverage   38.96%   39.24%   +0.27%     
==========================================
  Files         173      175       +2     
  Lines       18894    19011     +117     
  Branches      237      272      +35     
==========================================
+ Hits         7362     7460      +98     
- Misses      10617    10624       +7     
- Partials      915      927      +12

Impacted Files	Coverage Δ
ui/src/app/applications/components/utils.tsx	49.83% <0%> (ø)	⬆️
ui/src/app/shared/services/projects-service.ts	19.71% <0%> (ø)	⬆️
util/dex/dex.go	81.08% <0%> (ø)
util/dex/config.go	83.9% <0%> (ø)
server/cache/cache.go	88.23% <0%> (+2.86%)	⬆️

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