Config refactor split files

[rh-amarin]

Config Refactor based on proposed standard

This PR refactors the configuration system to use https://github.com/spf13/viper for more flexible and maintainable configuration management.

What Changed

• Configuration Framework: Migrated from environment variable-based config to viper-based system
• Command-Specific Config: Added specialized config structs for migrate and serve commands
• Config Endpoint: Added HTTP endpoint to expose runtime configuration
• Documentation: Comprehensive config documentation added

How to Review This PR

The commits are organized in a logical sequence to make reviewing easier. Review them in order:

1️⃣ Dependencies (Commit 1)

Files: go.mod, go.sum
Focus: Verify viper and related dependencies are appropriate

2️⃣ Documentation & Template (Commit 2)

Files: configs/config.yaml, docs/config.md
Focus:

• Review the config file structure and defaults
• Ensure documentation is clear and comprehensive
• Validate that all config options are documented

3️⃣ New Config Components (Commit 3)

Files: pkg/config/app.go, pkg/config/migrate_config.go, pkg/config/serve_config.go, tests
Focus:

• Review new config struct design
• Check test coverage for new components
• Validate command-specific config separation makes sense

4️⃣ Core Config Refactor (Commit 4)

Files: pkg/config/*.go
Focus:

• Review viper integration in existing config components
• Check backward compatibility with existing env vars
• Validate config loading and validation logic
• Review updated tests

5️⃣ Config Handlers (Commit 5)

Files: pkg/handlers/config.go, pkg/handlers/config_test.go
Focus:

• Review HTTP endpoint implementation
• Check security considerations (what config data is exposed)
• Validate test coverage

6️⃣ Environment Framework (Commit 6)

Files: cmd/hyperfleet-api/environments/*.go
Focus:

• Review environment-specific config changes
• Ensure simplification maintains necessary functionality

7️⃣ Command Updates (Commit 7)

Files: cmd/hyperfleet-api/migrate/cmd.go, cmd/hyperfleet-api/servecmd/cmd.go
Focus:

• Review how commands initialize and use new config system
• Check error handling

8️⃣ Server Components (Commit 8)

Files: cmd/hyperfleet-api/server/*.go
Focus:

• Review server initialization with new config
• Check that config endpoint is properly registered

9️⃣ Test Updates (Commit 9)

Files: test/helper.go, test/integration/*.go
Focus:

• Review test helper updates
• Ensure integration tests work with new config system

🔟 Build System (Commit 10)

Files: Makefile
Focus:

• Review Makefile changes
• Verify build and test targets still work correctly

Testing Checklist

• All unit tests pass
• Integration tests pass
• Config can be loaded from file
• Config can be loaded from environment variables
• Config validation works correctly
• Config endpoint returns expected data
• Backward compatibility with existing env vars maintained

Acceptance Criteria

• New viper-based config system is functional
• All existing functionality works with new config system
• Config documentation is complete
• Test coverage is maintained or improved
• No breaking changes to existing deployments

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