Add --ignore-unviable-attestations and deprecate --disable-last-epoch-targets (#16094)

This PR introduces flag `--ignore-unviable-attestations` (replaces and
deprecates `--disable-last-epoch-targets`) to drop attestations whose
target state is not viable; default remains to process them unless
explicitly enabled.

config/features/config.go

@@ -71,7 +71,7 @@ type Flags struct {
 
 	DisableResourceManager     bool // Disables running the node with libp2p's resource manager.
 	DisableStakinContractCheck bool // Disables check for deposit contract when proposing blocks
-	DisableLastEpochTargets    bool // Disables processing of states for attestations to old blocks.
+	IgnoreUnviableAttestations bool // Ignore attestations whose target state is not viable (avoids lagging-node DoS).
 
 	EnableVerboseSigVerification bool // EnableVerboseSigVerification specifies whether to verify individual signature if batch verification fails
 
@@ -281,9 +281,11 @@ func ConfigureBeaconChain(ctx *cli.Context) error {
 		logEnabled(blacklistRoots)
 		cfg.BlacklistedRoots = parseBlacklistedRoots(ctx.StringSlice(blacklistRoots.Name))
 	}
-	if ctx.IsSet(disableLastEpochTargets.Name) {
-		logEnabled(disableLastEpochTargets)
-		cfg.DisableLastEpochTargets = true
+
+	cfg.IgnoreUnviableAttestations = false
+	if ctx.IsSet(ignoreUnviableAttestations.Name) && ctx.Bool(ignoreUnviableAttestations.Name) {
+		logEnabled(ignoreUnviableAttestations)
+		cfg.IgnoreUnviableAttestations = true
 	}
 
 	if ctx.IsSet(EnableStateDiff.Name) {