fix: enable kubedog tracking with atomic/rollback-on-failure helm flags

[yxxhero]

Problem

When using atomic: true with trackMode: kubedog, the --atomic flag was passed to Helm which caused Helm to wait for resources and rollback internally before helmfile could start kubedog tracking. This prevented users from seeing deployment logs and errors during failed deployments.

Solution

Modified helmfile to skip passing --atomic to Helm when kubedog is enabled, and instead handle the rollback manually if kubedog tracking fails. This preserves atomic semantics while allowing kubedog to track resources.

Changes

• Add RollbackRelease method to helmexec.Interface and implementation to support manual rollback
• Add appendAtomicFlags function that intelligently skips --atomic when kubedog is enabled
• Add handleKubedogFailure function to execute rollback when kubedog tracking fails and atomic semantics are enabled
• Update flagsForUpgrade to use new atomic flag handling
• Add comprehensive tests for the new atomic flag behavior

Behavior

Before:

atomic: true + trackMode: kubedog
→ Helm waits for resources with --atomic
→ Failure occurs → Helm automatically rolls back
→ Returns error to helmfile
→ kubedog never starts ❌

After:

atomic: true + trackMode: kubedog
→ Helm upgrade runs (without --atomic)
→ kubedog starts tracking immediately ✅
→ If tracking fails → helmfile manually rolls back ✅
→ Atomic semantics preserved ✅

Testing

• Added TestAppendAtomicFlags with 7 test cases
• All existing tests pass
• make check passes (lint + vet)

Example

Users can now use this configuration:

helmDefaults:
  atomic: true
  trackMode: kubedog
  wait: true

And see kubedog tracking output even when deployments fail, with automatic rollback still working.

Fixes #2448