s3api: fix static IAM policy enforcement after reload (#8532)

* s3api: honor attached IAM policies over legacy actions

* s3api: hydrate IAM policy docs during config reload

* s3api: use policy-aware auth when listing buckets

* credential: propagate context through filer_etc policy reads

* credential: make legacy policy deletes durable

* s3api: exercise managed policy runtime loader

* s3api: allow static IAM users without session tokens

* iam: deny unmatched attached policies under default allow

* iam: load embedded policy files from filer store

* s3api: require session tokens for IAM presigning

* s3api: sync runtime policies into zero-config IAM

* credential: respect context in policy file loads

* credential: serialize legacy policy deletes

* iam: align filer policy store naming

* s3api: use authenticated principals for presigning

* iam: deep copy policy conditions

* s3api: require request creation in policy tests

* filer: keep ReadInsideFiler as the context-aware API

* iam: harden filer policy store writes

* credential: strengthen legacy policy serialization test

* credential: forward runtime policy loaders through wrapper

* s3api: harden runtime policy merging

* iam: require typed already-exists errors

weed/credential/filer_etc/filer_etc_store.go

@@ -20,6 +20,7 @@ type FilerEtcStore struct {
 	filerAddressFunc func() pb.ServerAddress // Function to get current active filer
 	grpcDialOption   grpc.DialOption
 	mu               sync.RWMutex // Protects filerAddressFunc and grpcDialOption
+	policyMu         sync.Mutex   // Serializes legacy managed-policy mutations
 }
 
 func (store *FilerEtcStore) GetName() credential.CredentialStoreTypeName {