Wait for Helm v4 before raising when platformCommand and Command are set

same for `PlatformHooks` and `hooks`.

When backporting a feature for Helm v3 we forgot to mark as deprecation
validations that will enforced in v4.

See (search for "Remove in Helm 4."):
- https://github.com/helm/helm/pull/13592/files#diff-fc137d62147eb6a9c89c0566479ff219320ca691f2505631ebacbe513bcc8108R268-R270

Fix:
Signed-off-by: Benoit Tigeot <benoit.tigeot@lifen.fr>
(cherry picked from commit 5d9d9a0fb8)

pkg/plugin/plugin.go

@@ -84,7 +84,7 @@ type Metadata struct {
 	PlatformCommand []PlatformCommand `json:"platformCommand"`
 
 	// Command is the plugin command, as a single string.
-	// Providing a command will result in an error if PlatformCommand is also set.
+	// Providing a command will result in an deprecation warning if PlatformCommand is also set.
 	//
 	// The command will be passed through environment expansion, so env vars can
 	// be present in this command. Unless IgnoreFlags is set, this will
@@ -266,11 +266,11 @@ func validatePluginData(plug *Plugin, filepath string) error {
 	plug.Metadata.Usage = sanitizeString(plug.Metadata.Usage)
 
 	if len(plug.Metadata.PlatformCommand) > 0 && len(plug.Metadata.Command) > 0 {
-		return fmt.Errorf("both platformCommand and command are set in %q", filepath)
+		fmt.Printf("both platformCommand and command are set in %q. It's deprecated and will not be possible in Helm v4\n", filepath)
 	}
 
 	if len(plug.Metadata.PlatformHooks) > 0 && len(plug.Metadata.Hooks) > 0 {
-		return fmt.Errorf("both platformHooks and hooks are set in %q", filepath)
+		fmt.Printf("both platformHooks and hooks are set in %q. It's deprecated and will not be possible in Helm v4\n", filepath)
 	}
 
 	// We could also validate SemVer, executable, and other fields should we so choose.

pkg/plugin/plugin_test.go

@@ -496,8 +496,8 @@ func TestValidatePluginData(t *testing.T) {
 		{false, mockMissingMeta},         // Test if the metadata section missing
 		{true, mockNoCommand},            // Test no command metadata works
 		{true, mockLegacyCommand},        // Test legacy command metadata works
-		{false, mockWithCommand},         // Test platformCommand and command both set fails
-		{false, mockWithHooks},           // Test platformHooks and hooks both set fails
+		{true, mockWithCommand},          // Test platformCommand and command both set pass until v4
+		{true, mockWithHooks},            // Test platformHooks and hooks both set pass until v4
 	} {
 		err := validatePluginData(item.plug, fmt.Sprintf("test-%d", i))
 		if item.pass && err != nil {