Add Veeam storage class override (#19748)

Recent Veeam is very picky about storage class names. Add `_MINIO_VEEAM_FORCE_SC` env var.

It will override the storage class returned by the storage backend if it is non-standard
and we detect a Veeam client by checking the User Agent.

Applies to HeadObject/GetObject/ListObject*

cmd/erasure-server-pool.go

@@ -1387,8 +1387,7 @@ func (z *erasureServerPools) ListObjectVersions(ctx context.Context, bucket, pre
 	// It requests unique blocks with a specific prefix.
 	// We skip scanning the parent directory for
 	// more objects matching the prefix.
-	ri := logger.GetReqInfo(ctx)
-	if ri != nil && strings.Contains(ri.UserAgent, `1.0 Veeam/1.0 Backup`) && strings.HasSuffix(prefix, ".blk") {
+	if isVeeamClient(ctx) && strings.HasSuffix(prefix, ".blk") {
 		opts.BaseDir = prefix
 		opts.Transient = true
 	}