fix: Update IAM config field name for role store configuration

- Change JSON field from 'roles' to 'roleStore' for clarity
- Prevents confusion with the actual role definitions array
- Matches the new distributed configuration schema

This ensures the JSON configuration properly maps to the
RoleStoreConfig struct for distributed IAM deployments.

weed/iam/integration/iam_manager.go

@@ -11,10 +11,10 @@ import (
 
 // IAMManager orchestrates all IAM components
 type IAMManager struct {
-	stsService    *sts.STSService
-	policyEngine  *policy.PolicyEngine
-	roleStore     RoleStore
-	initialized   bool
+	stsService   *sts.STSService
+	policyEngine *policy.PolicyEngine
+	roleStore    RoleStore
+	initialized  bool
 }
 
 // IAMConfig holds configuration for all IAM components