feat: add support for helm 4 --server-side upgrade flag (#2641)

* feat: add support for helm 4 --server-side upgrade flag

Add support for the helm 4 upgrade flag --server-side which accepts
"true", "false", or "auto" (default "auto"). This allows users to
explicitly control server-side apply behavior, which is needed for
releases originally installed with Helm 3 and being managed with Helm 4.

The flag can be configured via:
- CLI: --server-side flag on sync, apply, and diff commands
- helmDefaults.serverSide in helmfile.yaml
- releases[].serverSide per-release override

Precedence: release-level > CLI flag > helmDefaults.
Errors are returned when serverSide is set but running Helm 3, or when
an invalid value is provided.

Closes #2640

Signed-off-by: yxxhero <aiopsclub@163.com>

* test: update TestGenerateID expected hashes for new ServerSide field

Adding ServerSide *string to ReleaseSpec changes spew's %#v output and
shifts the FNV hash used by generateValuesID. Update the hard-coded want
values to the new deterministic hashes.

Signed-off-by: yxxhero <aiopsclub@163.com>

---------

Signed-off-by: yxxhero <aiopsclub@163.com>

pkg/state/temp_test.go

@@ -38,39 +38,39 @@ func TestGenerateID(t *testing.T) {
 	run(testcase{
 		subject: "baseline",
 		release: ReleaseSpec{Name: "foo", Chart: "incubator/raw"},
-		want:    "foo-values-7f6f8d74dd",
+		want:    "foo-values-56c9b878cf",
 	})
 
 	run(testcase{
 		subject: "different bytes content",
 		release: ReleaseSpec{Name: "foo", Chart: "incubator/raw"},
 		data:    []byte(`{"k":"v"}`),
-		want:    "foo-values-5fc74c864c",
+		want:    "foo-values-55d46b7dd4",
 	})
 
 	run(testcase{
 		subject: "different map content",
 		release: ReleaseSpec{Name: "foo", Chart: "incubator/raw"},
 		data:    map[string]any{"k": "v"},
-		want:    "foo-values-77df88dd65",
+		want:    "foo-values-8c574f646",
 	})
 
 	run(testcase{
 		subject: "different chart",
 		release: ReleaseSpec{Name: "foo", Chart: "stable/envoy"},
-		want:    "foo-values-77c96457f7",
+		want:    "foo-values-664cdfb57d",
 	})
 
 	run(testcase{
 		subject: "different name",
 		release: ReleaseSpec{Name: "bar", Chart: "incubator/raw"},
-		want:    "bar-values-6695f7ff4c",
+		want:    "bar-values-fbb5fd45b",
 	})
 
 	run(testcase{
 		subject: "specific ns",
 		release: ReleaseSpec{Name: "foo", Chart: "incubator/raw", Namespace: "myns"},
-		want:    "myns-foo-values-9b9484d4c",
+		want:    "myns-foo-values-7db84f99b",
 	})
 
 	for id, n := range ids {