feat: Using secret to attach identity to pod for observability publisher

[tiopramayudi]

Description

Since we are trying to move away from cloud-specific feature, hence as first step in observability publisher is to use secret for propagate identity instead of using existing workload identity way

Modifications

Add GOOGLE_APPLICATION_CREDENTIALS for propagate google identity to pod

Tests

Checklist

• Added PR label
• Added unit test, integration, and/or e2e tests
• Tested locally
• Updated documentation
• Update Swagger spec if the PR introduce API changes
• Regenerated Golang and Python client if the PR introduces API changes

Release Notes

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 60.75%. Comparing base (7caf48a) to head (b0040f3).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #607      +/-   ##
==========================================
+ Coverage   60.70%   60.75%   +0.04%     
==========================================
  Files         275      276       +1     
  Lines       22171    22205      +34     
==========================================
+ Hits        13460    13491      +31     
- Misses       7847     7849       +2     
- Partials      864      865       +1     

Flag	Coverage Δ
api-test	58.73% <ø> (+0.05%)	⬆️
sdk-test-3.10	75.51% <ø> (ø)
sdk-test-3.8	75.49% <ø> (ø)
sdk-test-3.9	75.49% <ø> (ø)

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[deadlycoconuts]

Thanks a lot for the changes @tiopramayudi ! I just left a couple of tiny comments but the main one's about removing the support for workload identity completely 🤔 (If it's not the scope of this MR or if it's something that isn't planned it's okay too 😅)