feat: add unit tests for config package

[Denyme24]

What this PR does / why we need it:

It adds comprehensive unit tests for the config package, which previously had zero test coverage. The config package is critical as it handles loading configuration files, applying defaults, and setting up controller-runtime options for the trainer controller manager.

Test Coverage Includes

• Configuration loading from YAML files with proper error handling
• Default value application when a config file is not provided
• Validation of configuration values (webhook ports, QPS/burst limits, concurrency settings)
• Controller-runtime options setup (metrics, webhooks, health probes, leader election)
• Edge cases and error scenarios

Additional Fix

While writing the tests, I discovered and fixed a missing default value for Webhook.Host in defaults.go, which could have led to nil pointer issues at runtime.

Coverage

• 98.2% of config package statements

Fixes #3081

Checklist:

• Docs included if any changes are user facing

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[Copilot]

Pull request overview

This PR adds comprehensive unit tests for the config package, which previously had zero test coverage. The config package is critical for loading configuration files, applying defaults, and setting up controller-runtime options.

Changes:

• Added 653 lines of unit tests covering configuration loading, validation, defaults application, and controller-runtime options setup
• Fixed a potential nil pointer dereference by adding a default value for Webhook.Host in defaults.go
• Achieved 98.2% test coverage for the config package

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
pkg/config/config_test.go	New comprehensive test suite covering all config package functions including file loading, validation, defaults, and integration tests
pkg/apis/config/v1alpha1/defaults.go	Added default value for Webhook.Host to prevent nil pointer dereference

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[andreyvelich]

Thanks for this @Denyme24, we already have open PR to add unit tests for Trainer config: #2893
@kapil27 Are you still working on #2893 to address the review changes?

[kapil27]

Yes @andreyvelich , I will address those comments.