Add flag for custom slasher database directory (#11890)

* Add slasher database directory flag

* Fix up some beacon chain flag uses

* fmt

Co-authored-by: rauljordan <raul@prysmaticlabs.com>
Co-authored-by: prylabs-bulldozer[bot] <58059840+prylabs-bulldozer[bot]@users.noreply.github.com>

cmd/beacon-chain/flags/base.go

@@ -5,6 +5,7 @@ package flags
 import (
 	"strings"
 
+	"github.com/prysmaticlabs/prysm/v3/cmd"
 	"github.com/prysmaticlabs/prysm/v3/config/params"
 	"github.com/urfave/cli/v2"
 )
@@ -246,4 +247,10 @@ var (
 			"WARNING: This flag should be used only if you have a clear understanding that community has decided to override the terminal block hash activation epoch. " +
 			"Incorrect usage will result in your node experience consensus failure.",
 	}
+	// SlasherDirFlag defines a path on disk where the slasher database is stored.
+	SlasherDirFlag = &cli.StringFlag{
+		Name:  "slasher-datadir",
+		Usage: "Directory for the slasher database",
+		Value: cmd.DefaultDataDir(),
+	}
 )