Use functional options for --blob-retention-epochs (#13283)

* blob retention period functional opts

* missed unstaged change

* missed other init after cleardb

* fix ineffassign

* fix dup import

* config failsafe for tests

---------

Co-authored-by: Kasey Kirkham <kasey@users.noreply.github.com>

cmd/beacon-chain/flags/base.go

@@ -265,10 +265,4 @@ var (
 		Usage: "Directory for the slasher database",
 		Value: cmd.DefaultDataDir(),
 	}
-	BlobRetentionEpoch = &cli.Uint64Flag{
-		Name:    "blob-retention-epochs",
-		Usage:   "Override the default blob retention period (measured in epochs). The node will exit with an error at startup if the value is less than the default of 4096 epochs.",
-		Value:   uint64(params.BeaconNetworkConfig().MinEpochsForBlobsSidecarsRequest),
-		Aliases: []string{"extend-blob-retention-epoch"},
-	}
 )