feat: add helm-legacy track mode for Helm v4 compatibility (#2466)

Add support for trackMode: helm-legacy to use Helm v4's --wait=legacy flag,
which maintains compatibility with Helm v3's wait behavior during migration.

Helm v4 changed the default --wait behavior from polling to a watcher-based
approach. This can cause issues with charts that have broken livenessProbe
configurations without startupProbe. The --wait=legacy flag preserves the
Helm v3 polling behavior for smoother migration.

Changes:
- Add TrackModeHelmLegacy constant in pkg/kubedog/options.go
- Use kubedog.TrackMode constants instead of raw strings in helmx.go
- Enhance appendWaitFlags to use --wait=legacy for Helm v4 when trackMode
  is helm-legacy
- Add nil check for logger before logging warning
- Add version check with warning when helm-legacy is used with Helm v3
- Update validation in pkg/config to accept helm-legacy track mode
- Update command-line flags in cmd/apply.go and cmd/sync.go
- Add comprehensive documentation in docs/advanced-features.md
- Add thorough test coverage including warning message verification

Behavior:
- Helm v4 + helm-legacy: Uses --wait=legacy
- Helm v3 + helm-legacy: Falls back to --wait with warning
- Helm v4 + helm: Uses --wait (watcher mode)
- Any + kubedog: Skips --wait flag

Fixes #2464

Signed-off-by: yxxhero <aiopsclub@163.com>
Co-authored-by: Copilot <copilot@github.com>

pkg/state/state.go

@@ -3439,7 +3439,7 @@ func (st *HelmState) flagsForUpgrade(helm helmexec.Interface, release *ReleaseSp
 	flags = st.appendChartVersionFlags(flags, release)
 	flags = st.appendEnableDNSFlags(flags, release)
 
-	flags = st.appendWaitFlags(flags, release, opt)
+	flags = st.appendWaitFlags(flags, helm, release, opt)
 	flags = st.appendWaitForJobsFlags(flags, release, opt)
 
 	// non-OCI chart should be verified here