Add missing --timeout flag to helmfile sync command with documentation (#2148)

* Initial plan

* Implement --timeout flag for helmfile sync command

- Add Timeout field to SyncOptions struct in pkg/config/sync.go
- Add --timeout flag to sync command in cmd/sync.go
- Add Timeout field to SyncOpts struct in pkg/state/state.go
- Modify timeoutFlags() function to prioritize CLI timeout over release and default configs
- Add test case to verify CLI timeout overrides other timeout settings
- Follow same pattern as existing --wait and --wait-for-jobs flags

Co-authored-by: yxxhero <11087727+yxxhero@users.noreply.github.com>

* Fix lint issues: format test struct fields properly

Co-authored-by: yxxhero <11087727+yxxhero@users.noreply.github.com>

* Update docs: Add --timeout flag documentation for helmfile sync command

Co-authored-by: yxxhero <11087727+yxxhero@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: yxxhero <11087727+yxxhero@users.noreply.github.com>

pkg/state/state_test.go

@@ -170,6 +170,7 @@ func TestHelmState_flagsForUpgrade(t *testing.T) {
 		version  *semver.Version
 		defaults HelmSpec
 		release  *ReleaseSpec
+		syncOpts *SyncOpts
 		want     []string
 		wantErr  string
 	}{
@@ -455,6 +456,27 @@ func TestHelmState_flagsForUpgrade(t *testing.T) {
 				"--namespace", "test-namespace",
 			},
 		},
+		{
+			name: "timeout-from-cli-flag",
+			defaults: HelmSpec{
+				Timeout: 123,
+			},
+			release: &ReleaseSpec{
+				Chart:     "test/chart",
+				Version:   "0.1",
+				Timeout:   some(456),
+				Name:      "test-charts",
+				Namespace: "test-namespace",
+			},
+			syncOpts: &SyncOpts{
+				Timeout: 789,
+			},
+			want: []string{
+				"--version", "0.1",
+				"--timeout", "789s",
+				"--namespace", "test-namespace",
+			},
+		},
 		{
 			name: "atomic",
 			defaults: HelmSpec{
@@ -737,7 +759,7 @@ func TestHelmState_flagsForUpgrade(t *testing.T) {
 				Version: tt.version,
 			}
 
-			args, _, err := state.flagsForUpgrade(helm, tt.release, 0, nil)
+			args, _, err := state.flagsForUpgrade(helm, tt.release, 0, tt.syncOpts)
 			if err != nil && tt.wantErr == "" {
 				t.Errorf("unexpected error flagsForUpgrade: %v", err)
 			}