feat: add concurrency limiter to scoutfs

This brings scoutfs in-line with the posix concurrency limiter.
This fixes a hang with scoutfs due to not correctly initializing
the concurrency in posix leading to a concurrency of 0 allowed.

This also adds a sane default to the posix concurrency when not
initialized.

cmd/versitygw/scoutfs.go

@@ -99,6 +99,13 @@ move interfaces as well as support for tiered filesystems.`,
 				EnvVars:     []string{"VGW_DISABLE_NOARCHIVE"},
 				Destination: &disableNoArchive,
 			},
+			&cli.IntFlag{
+				Name:        "concurrency",
+				Usage:       "maximum concurrent actions allowed",
+				EnvVars:     []string{"VGW_POSIX_CONCURRENCY"},
+				Value:       5000,
+				Destination: &actionsConcurrency,
+			},
 		},
 	}
 }
@@ -112,6 +119,10 @@ func runScoutfs(ctx *cli.Context) error {
 		return fmt.Errorf("invalid directory permissions: %d", dirPerms)
 	}
 
+	if actionsConcurrency <= 0 {
+		return fmt.Errorf("concurrency must be positive, got %d", actionsConcurrency)
+	}
+
 	var opts scoutfs.ScoutfsOpts
 	opts.GlacierMode = glacier
 	opts.ChownUID = chownuid
@@ -122,6 +133,7 @@ func runScoutfs(ctx *cli.Context) error {
 	opts.VersioningDir = versioningDir
 	opts.ValidateBucketNames = disableStrictBucketNames
 	opts.SetProjectID = setProjectID
+	opts.Concurrency = actionsConcurrency
 
 	be, err := scoutfs.New(ctx.Args().Get(0), opts)
 	if err != nil {