Native support for Gnosis Beacon Chain network (#2931)

## Proposed Changes

Add a new hardcoded spec for the Gnosis Beacon Chain.
Ideally, official Lighthouse executables will be able to connect to the gnosis beacon chain from now on, using `--network gnosis` CLI option.

common/eth2_network_config/built_in_network_configs/gnosis/boot_enr.yaml

@@ -0,0 +1,5 @@
+# Gnosis Chain Team
+- enr:-IS4QGmLwm7gFd0L0CEisllrb1op3v-wAGSc7_pwSMGgN3bOS9Fz7m1dWbwuuPHKqeETz9MbhjVuoWk0ohkyRv98kVoBgmlkgnY0gmlwhGjtlgaJc2VjcDI1NmsxoQLMdh0It9fJbuiLydZ9fpF6MRzgNle0vODaDiMqhbC7WIN1ZHCCIyg
+- enr:-IS4QFUVG3dvLPCUEI7ycRvFm0Ieg_ITa5tALmJ9LI7dJ6ieT3J4fF9xLRjOoB4ApV-Rjp7HeLKzyTWG1xRdbFBNZPQBgmlkgnY0gmlwhErP5weJc2VjcDI1NmsxoQOBbaJBvx0-w_pyZUhQl9A510Ho2T0grE0K8JevzES99IN1ZHCCIyg
+- enr:-Ku4QOQk8V-Hu2gxFzRXmLYIO4AvWDZhoMFwTf3n3DYm_mbsWv0ZitoqiN6JZUUj6Li6e1Jk1w2zFSVHKPMUP1g5tsgBh2F0dG5ldHOIAAAAAAAAAACEZXRoMpD5Jd3FAAAAZP__________gmlkgnY0gmlwhC1PTpmJc2VjcDI1NmsxoQL1Ynt5PoA0UOcHa1Rfn98rmnRlLzNuWTePPP4m4qHVroN1ZHCCKvg
+- enr:-Ku4QFaTwgoms-EiiRIfHUH3FXprWUFgjHg4UuWvilqoUQtDbmTszVIxUEOwQUmA2qkiP-T9wXjc_rVUuh9cU7WgwbgBh2F0dG5ldHOIAAAAAAAAAACEZXRoMpD5Jd3FAAAAZP__________gmlkgnY0gmlwhC0hBmCJc2VjcDI1NmsxoQOpsg1XCrXmCwZKcSTcycLwldoKUMHPUpMEVGeg_EEhuYN1ZHCCKvg

common/eth2_network_config/built_in_network_configs/gnosis/config.yaml

@@ -0,0 +1,85 @@
+# Gnosis Beacon Chain config
+
+# Extends the gnosis preset
+PRESET_BASE: 'gnosis'
+
+# Transition
+# ---------------------------------------------------------------
+# TBD, 2**256-2**10 is a placeholder
+TERMINAL_TOTAL_DIFFICULTY: 115792089237316195423570985008687907853269984665640564039457584007913129638912
+# By default, don't use these params
+TERMINAL_BLOCK_HASH: 0x0000000000000000000000000000000000000000000000000000000000000000
+TERMINAL_BLOCK_HASH_ACTIVATION_EPOCH: 18446744073709551615
+
+# Genesis
+# ---------------------------------------------------------------
+# `2**12` (= 4,096)
+MIN_GENESIS_ACTIVE_VALIDATOR_COUNT: 4096
+# Dec 8, 2021, 13:00 UTC
+MIN_GENESIS_TIME: 1638968400
+# Gnosis Beacon Chain initial fork version
+GENESIS_FORK_VERSION: 0x00000064
+# 6000 seconds (100 minutes)
+GENESIS_DELAY: 6000
+
+
+# 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: 0x01000064
+ALTAIR_FORK_EPOCH: 512
+# Merge
+BELLATRIX_FORK_VERSION: 0x02000064
+BELLATRIX_FORK_EPOCH: 18446744073709551615
+# Sharding
+SHARDING_FORK_VERSION: 0x03000064
+SHARDING_FORK_EPOCH: 18446744073709551615
+
+# TBD, 2**32 is a placeholder. Merge transition approach is in active R&D.
+TRANSITION_TOTAL_DIFFICULTY: 4294967296
+
+
+# Time parameters
+# ---------------------------------------------------------------
+# 5 seconds
+SECONDS_PER_SLOT: 5
+# 6 (estimate from Gnosis Chain)
+SECONDS_PER_ETH1_BLOCK: 6
+# 2**8 (= 256) epochs ~8 hours
+MIN_VALIDATOR_WITHDRAWABILITY_DELAY: 256
+# 2**8 (= 256) epochs ~8 hours
+SHARD_COMMITTEE_PERIOD: 256
+# 2**10 (= 1024) ~1.4 hour
+ETH1_FOLLOW_DISTANCE: 1024
+
+
+# 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**12 (= 4096)
+CHURN_LIMIT_QUOTIENT: 4096
+
+
+# Fork choice
+# ---------------------------------------------------------------
+# TODO: enable once proposer boosting is desired on mainnet
+# 70%
+# PROPOSER_SCORE_BOOST: 70
+
+# Deposit contract
+# ---------------------------------------------------------------
+# Gnosis Chain
+DEPOSIT_CHAIN_ID: 100
+DEPOSIT_NETWORK_ID: 100
+DEPOSIT_CONTRACT_ADDRESS: 0x0B98057eA310F4d31F2a452B414647007d1645d9

common/eth2_network_config/built_in_network_configs/gnosis/deploy_block.txt

@@ -0,0 +1 @@
+19469077

common/eth2_network_config/src/lib.rs

@@ -226,7 +226,7 @@ mod tests {
     use super::*;
     use ssz::Encode;
     use tempfile::Builder as TempBuilder;
-    use types::{Config, Eth1Data, Hash256, MainnetEthSpec};
+    use types::{Config, Eth1Data, GnosisEthSpec, Hash256, MainnetEthSpec, GNOSIS};
 
     type E = MainnetEthSpec;
 
@@ -263,7 +263,11 @@ mod tests {
                 .unwrap_or_else(|_| panic!("{:?}", net.name));
 
             // Ensure we can parse the YAML config to a chain spec.
-            config.chain_spec::<MainnetEthSpec>().unwrap();
+            if net.name == GNOSIS {
+                config.chain_spec::<GnosisEthSpec>().unwrap();
+            } else {
+                config.chain_spec::<MainnetEthSpec>().unwrap();
+            }
 
             assert_eq!(
                 config.genesis_state_bytes.is_some(),