fix: case-insensitive lookups for metadata (#11489)

continuation of #11487, with more changes

cmd/erasure-object.go

@@ -179,7 +179,7 @@ func (er erasureObjects) GetObjectNInfo(ctx context.Context, bucket, object stri
 	}
 	if objInfo.TransitionStatus == lifecycle.TransitionComplete {
 		// If transitioned, stream from transition tier unless object is restored locally or restore date is past.
-		restoreHdr, ok := getMapValue(objInfo.UserDefined, xhttp.AmzRestore)
+		restoreHdr, ok := caseInsensitiveMap(objInfo.UserDefined).Lookup(xhttp.AmzRestore)
 		if !ok || !strings.HasPrefix(restoreHdr, "ongoing-request=false") || (!objInfo.RestoreExpires.IsZero() && time.Now().After(objInfo.RestoreExpires)) {
 			return getTransitionedObjectReader(ctx, bucket, object, rs, h, objInfo, opts)
 		}