cmd/geth: add support for sepolia testnet (#23730)

* cmd/geth: add support for sepolia testnet

* core: last details on sepolia genesis

* params: fix sepolia hash + reduce testing code

* Update params/bootnodes.go

* cmd/geth: fix attach path for sepolia

* params: update bootnodes

* params: fix

* core: fix docstring

* params: add sepolia CHT

core/genesis.go

@@ -244,6 +244,8 @@ func (g *Genesis) configOrDefault(ghash common.Hash) *params.ChainConfig {
 		return params.MainnetChainConfig
 	case ghash == params.RopstenGenesisHash:
 		return params.RopstenChainConfig
+	case ghash == params.SepoliaGenesisHash:
+		return params.SepoliaChainConfig
 	case ghash == params.RinkebyGenesisHash:
 		return params.RinkebyChainConfig
 	case ghash == params.GoerliGenesisHash:
@@ -400,6 +402,19 @@ func DefaultGoerliGenesisBlock() *Genesis {
 	}
 }
 
+// DefaultSepoliaGenesisBlock returns the Sepolia network genesis block.
+func DefaultSepoliaGenesisBlock() *Genesis {
+	return &Genesis{
+		Config:     params.SepoliaChainConfig,
+		Nonce:      0,
+		ExtraData:  []byte("Sepolia, Athens, Attica, Greece!"),
+		GasLimit:   0x1c9c380,
+		Difficulty: big.NewInt(0x20000),
+		Timestamp:  1633267481,
+		Alloc:      decodePrealloc(sepoliaAllocData),
+	}
+}
+
 // DeveloperGenesisBlock returns the 'geth --dev' genesis block.
 func DeveloperGenesisBlock(period uint64, faucet common.Address) *Genesis {
 	// Override the default period to the user requested one