Decrease proposer boost to 40% (#3201)

## Issue Addressed

https://github.com/ethereum/consensus-specs/pull/2895

## Proposed Changes

Lower the proposer boost to 40%, which is a trade-off against different types of attacks.

## Additional Info

This PR also enables proposer boost on Ropsten assuming that this PR will be merged: https://github.com/eth-clients/merge-testnets/pull/10

common/eth2_network_config/built_in_network_configs/gnosis/config.yaml

@@ -74,8 +74,8 @@ CHURN_LIMIT_QUOTIENT: 4096
 
 # Fork choice
 # ---------------------------------------------------------------
-# 70%
-PROPOSER_SCORE_BOOST: 70
+# 40%
+PROPOSER_SCORE_BOOST: 40
 
 # Deposit contract
 # ---------------------------------------------------------------

common/eth2_network_config/built_in_network_configs/mainnet/config.yaml

@@ -74,8 +74,8 @@ CHURN_LIMIT_QUOTIENT: 65536
 
 # Fork choice
 # ---------------------------------------------------------------
-# 70%
-PROPOSER_SCORE_BOOST: 70
+# 40%
+PROPOSER_SCORE_BOOST: 40
 
 # Deposit contract
 # ---------------------------------------------------------------

common/eth2_network_config/built_in_network_configs/prater/config.yaml

@@ -74,8 +74,8 @@ CHURN_LIMIT_QUOTIENT: 65536
 
 # Fork choice
 # ---------------------------------------------------------------
-# 70%
-PROPOSER_SCORE_BOOST: 70
+# 40%
+PROPOSER_SCORE_BOOST: 40
 
 # Deposit contract
 # ---------------------------------------------------------------

common/eth2_network_config/built_in_network_configs/ropsten/config.yaml

@@ -59,6 +59,11 @@ MIN_PER_EPOCH_CHURN_LIMIT: 4
 CHURN_LIMIT_QUOTIENT: 65536
 
 
+# Fork choice
+# ---------------------------------------------------------------
+# 40%
+PROPOSER_SCORE_BOOST: 40
+
 # Deposit contract
 # ---------------------------------------------------------------
 DEPOSIT_CHAIN_ID: 3