Fix controller-manager failures causing CNS to remain incorrectly healthy

[Copilot]

Problem

Currently, CNS will repeatedly try to start controller-manager even if it encounters terminal errors, keeping CNS in an incorrectly healthy state. This affects both controller-manager in CRD mode and multiTenantController in MultiTenantCRD mode.

Solution

This PR adds timeouts for controller startup and proper error handling to ensure CNS fails appropriately when controllers can't be started. Key changes:

1. Added timeout contexts for both controller-manager and multiTenantController with a 5-minute default
2. Added new metrics to track timeout occurrences:
   • cns_ctrlmanager_start_timeouts_total
   • cns_multitenantcontroller_start_timeouts_total
3. Made CNS handle terminal errors more gracefully by propagating errors through channels instead of calling os.Exit directly from goroutines
4. Simplified goroutine structure for starting controllers and improved error reporting
5. Extracted common functionality to reusable functions for better maintainability

Before

• CNS would indefinitely retry controller-manager.Start on failures
• No timeout was set for controller startup attempts
• Terminal errors wouldn't cause CNS to fail appropriately

After

• Controller startup attempts have a reasonable timeout
• Terminal errors are properly propagated and handled
• CNS will report unhealthy status when controllers fail to start

These changes ensure CNS will not remain in an incorrectly healthy state when controllers fail to initialize properly.

Fixes #3687.

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