feat(service): add external secrets to creation flow

[rmnbrd]

Summary

⚠️ Based on #2719

Adds external secrets support during service creation, including variable flow data, summary rendering, secret manager selection helpers, and the add-secret modal used by app/container/job creation flows.

Screenshots / Recordings

Testing

• Changes tested locally in the relevant Console's pages and Storybooks
• yarn test or yarn test -u (if you need to regenerate snapshots)
• yarn format
• yarn lint

PR Checklist

• I followed naming, styling, and TypeScript rules (see .cursor/rules)
• I performed a self-review (diff inspected, dead code removed)
• I titled the PR using Conventional Commits with a scope when possible (e.g. feat(service): add new Terraform service) - required for semantic-release
• I only kept necessary comments, written in English (watch for useless AI comments)
• I involved a designer to validate UI changes if I am not a designer
• I covered new business logic with tests (unit)
• I confirmed CI is green (Codecov red can be accepted)
• I reviewed and executed locally any AI-assisted code

[Copilot]

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[codecov]

Codecov Report

❌ Patch coverage is 19.48052% with 186 lines in your changes missing coverage. Please review.
✅ Project coverage is 45.50%. Comparing base (02e9796) to head (ad0a150).

Files with missing lines	Patch %	Lines
...rnal-secrets/add-secret-modal/add-secret-modal.tsx	0.00%	65 Missing ⚠️
...tainer-variables/step-variables/step-variables.tsx	28.20%	41 Missing and 15 partials ⚠️
...te-variable-modal/create-update-variable-modal.tsx	25.00%	34 Missing and 2 partials ⚠️
.../external-secrets/use-variables-secret-managers.ts	0.00%	11 Missing ⚠️
...ummary-view/application-container-summary-view.tsx	33.33%	0 Missing and 6 partials ⚠️
...on-container-summary/step-summary/step-summary.tsx	57.14%	1 Missing and 5 partials ⚠️
...ib/job-creation-flow/step-summary/step-summary.tsx	0.00%	3 Missing ⚠️
...ob-creation-flow/step-variables/step-variables.tsx	0.00%	2 Missing ⚠️
...e/src/lib/job-creation-flow/template-form-sync.tsx	0.00%	1 Missing ⚠️

Additional details and impacted files

@@                              Coverage Diff                               @@
##           feat/secrets-manager-cluster-creation-flow    #2720      +/-   ##
==============================================================================
- Coverage                                       45.58%   45.50%   -0.08%     
==============================================================================
  Files                                             707     1151     +444     
  Lines                                           17731    24578    +6847     
  Branches                                         5338     7300    +1962     
==============================================================================
+ Hits                                             8082    11185    +3103     
- Misses                                           8198    11401    +3203     
- Partials                                         1451     1992     +541     

Flag	Coverage Δ
unittests	45.50% <19.48%> (-0.08%)	⬇️

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