Add sepolia config (sigp#3268)

## Issue Addressed

N/A

## Proposed Changes

Add network config for sepolia from eth-clients/merge-testnets#14

common/eth2_config/src/lib.rs

@@ -238,5 +238,6 @@ define_hardcoded_nets!(
     (prater, "prater", GENESIS_STATE_IS_KNOWN),
     (gnosis, "gnosis", GENESIS_STATE_IS_KNOWN),
     (kiln, "kiln", GENESIS_STATE_IS_KNOWN),
-    (ropsten, "ropsten", GENESIS_STATE_IS_KNOWN)
+    (ropsten, "ropsten", GENESIS_STATE_IS_KNOWN),
+    (sepolia, "sepolia", GENESIS_STATE_IS_KNOWN)
 );

common/eth2_network_config/built_in_network_configs/sepolia/boot_enr.yaml

@@ -0,0 +1 @@
+- enr:-Iq4QMCTfIMXnow27baRUb35Q8iiFHSIDBJh6hQM5Axohhf4b6Kr_cOCu0htQ5WvVqKvFgY28893DHAg8gnBAXsAVqmGAX53x8JggmlkgnY0gmlwhLKAlv6Jc2VjcDI1NmsxoQK6S-Cii_KmfFdUJL2TANL3ksaKUnNXvTCv1tLwXs0QgIN1ZHCCIyk

common/eth2_network_config/built_in_network_configs/sepolia/config.yaml

@@ -0,0 +1,76 @@
+# Extends the mainnet preset
+PRESET_BASE: 'mainnet'
+CONFIG_NAME: 'sepolia'
+
+# Genesis
+# ---------------------------------------------------------------
+MIN_GENESIS_ACTIVE_VALIDATOR_COUNT: 1300
+# Sunday, June 19, 2022 2:00:00 PM +UTC
+MIN_GENESIS_TIME: 1655647200
+GENESIS_FORK_VERSION: 0x90000069
+GENESIS_DELAY: 86400
+
+
+# Forking
+# ---------------------------------------------------------------
+# Some forks are disabled for now:
+#  - These may be re-assigned to another fork-version later
+#  - Temporarily set to max uint64 value: 2**64 - 1
+
+# Altair
+ALTAIR_FORK_VERSION: 0x90000070
+ALTAIR_FORK_EPOCH: 50
+
+# Merge
+BELLATRIX_FORK_VERSION: 0x90000071
+BELLATRIX_FORK_EPOCH: 100
+TERMINAL_TOTAL_DIFFICULTY: 100000000000000000000000
+TERMINAL_BLOCK_HASH: 0x0000000000000000000000000000000000000000000000000000000000000000
+TERMINAL_BLOCK_HASH_ACTIVATION_EPOCH: 18446744073709551615
+
+# Capella
+CAPELLA_FORK_VERSION: 0x03001020
+CAPELLA_FORK_EPOCH: 18446744073709551615
+
+# Sharding
+SHARDING_FORK_VERSION: 0x04001020
+SHARDING_FORK_EPOCH: 18446744073709551615
+
+# Time parameters
+# ---------------------------------------------------------------
+# 12 seconds
+SECONDS_PER_SLOT: 12
+# 14 (estimate from Eth1 mainnet)
+SECONDS_PER_ETH1_BLOCK: 14
+# 2**8 (= 256) epochs ~27 hours
+MIN_VALIDATOR_WITHDRAWABILITY_DELAY: 256
+# 2**8 (= 256) epochs ~27 hours
+SHARD_COMMITTEE_PERIOD: 256
+# 2**11 (= 2,048) Eth1 blocks ~8 hours
+ETH1_FOLLOW_DISTANCE: 2048
+
+
+# Validator cycle
+# ---------------------------------------------------------------
+# 2**2 (= 4)
+INACTIVITY_SCORE_BIAS: 4
+# 2**4 (= 16)
+INACTIVITY_SCORE_RECOVERY_RATE: 16
+# 2**4 * 10**9 (= 16,000,000,000) Gwei
+EJECTION_BALANCE: 16000000000
+# 2**2 (= 4)
+MIN_PER_EPOCH_CHURN_LIMIT: 4
+# 2**16 (= 65,536)
+CHURN_LIMIT_QUOTIENT: 65536
+
+
+# Fork choice
+# ---------------------------------------------------------------
+# 40%
+PROPOSER_SCORE_BOOST: 40
+
+# Deposit contract
+# ---------------------------------------------------------------
+DEPOSIT_CHAIN_ID: 11155111
+DEPOSIT_NETWORK_ID: 11155111
+DEPOSIT_CONTRACT_ADDRESS: 0x7f02C3E3c98b133055B8B348B2Ac625669Ed295D

common/eth2_network_config/built_in_network_configs/sepolia/deploy_block.txt

@@ -0,0 +1 @@
+1273020