feat: Add AuthRequired to Tool Manifest (#433)

Add `AuthRequired` to Tool Manifest so SDK could throw an error early
for unauthorized Tool invocations.
SDK changes:
https://github.com/googleapis/mcp-toolbox-sdk-python/pull/72/files

Also added `authRequired` to Neo4j and dgraph tools.

internal/server/config.go

@@ -316,6 +316,11 @@ func (c *ToolConfigs) UnmarshalYAML(ctx context.Context, unmarshal func(interfac
 			return fmt.Errorf("unable to unmarshal %q: %w", name, err)
 		}
 
+		// Make `authRequired` an empty list instead of nil for Tool manifest
+		if v["authRequired"] == nil {
+			v["authRequired"] = []string{}
+		}
+
 		kind, ok := v["kind"]
 		if !ok {
 			return fmt.Errorf("missing 'kind' field for %q", name)