Fix G204: replace os/exec with utilexec to address command injection warnings

[bcho]

Summary

• Refactors pkg/status/collector.go and pkg/auth/auth.go to use k8s.io/utils/exec (utilexec) instead of os/exec directly, eliminating gosec G204 (subprocess launched with variable) findings.
• Injects utilexec.Interface into Collector and AuthProvider structs, improving testability via dependency injection.

Resolves https://github.com/Azure/AKSFlexNode/security/code-scanning/101
Resolves https://github.com/Azure/AKSFlexNode/security/code-scanning/4

[Copilot]

Pull request overview

Refactors command execution in the status collector and auth provider to use k8s.io/utils/exec (utilexec) instead of os/exec, aiming to eliminate gosec G204 findings and enable easier mocking via an injected exec interface.

Changes:

• Added a utilexec.Interface field to status.Collector and auth.AuthProvider, defaulting to utilexec.New() in constructors.
• Updated status command execution to call c.exec.CommandContext(...) instead of exec.CommandContext(...).
• Updated Azure CLI invocation to use a.exec.CommandContext(...) and switched interactive stdio wiring to SetStdin/SetStdout/SetStderr.

Reviewed changes

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

File	Description
pkg/status/collector.go	Introduces utilexec.Interface on Collector and routes runCommand through it.
pkg/auth/auth.go	Introduces utilexec.Interface on AuthProvider and updates Azure CLI command creation + interactive stdio setup.

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