fix: capture Run() error in metrics controller goroutine

[abhaygoudannavar]

What this PR does

Fixes a closure bug where the metrics controller goroutine logged the wrong error on failure.

Problem

In main.go (lines 280-285), the goroutine that runs the metrics controller never captures the return value of metricsController.Run(). Instead, it references the outer err variable from the metrics.NewController() call:

metricsController, err := metrics.NewController(kruisegameInformerFactory)
if err != nil {
    setupLog.Error(err, "unable to create metrics controller")
    os.Exit(1)
}
kruisegameInformerFactory.Start(signal.Done())
go func() {
    if metricsController.Run(signal) != nil {
        setupLog.Error(err, "unable to setup metrics controller")  // wrong err
        os.Exit(1)
    }
}()

Since NewController succeeded (otherwise we'd have exited), err is nil by the time the goroutine runs. So if Run() fails, the log prints a nil error — making the failure impossible to diagnose.

Fix
Capture the return value of Run() into its own variable:

    if runErr := metricsController.Run(signal); runErr != nil {
        setupLog.Error(runErr, "unable to setup metrics controller")
        os.Exit(1)
    }
}()

fixes #325

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 40.53%. Comparing base (0974487) to head (f4c1adf).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #326   +/-   ##
=======================================
  Coverage   40.53%   40.53%           
=======================================
  Files         112      112           
  Lines       12547    12547           
=======================================
  Hits         5086     5086           
  Misses       7051     7051           
  Partials      410      410           

Flag	Coverage Δ
unittests	40.53% <ø> (ø)

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