Configure custom node submission handling of high risk transactions

[nlordell]

This PR introduces a new flag --disable-high-risk-public-mempool-transactions which controls whether or not "high-risk" transactions (i.e. transactions that interact with AMMs and can revert due to price movement and have MEV extracted from it) should be disabled for public mempool submission strategy.

Previously, we had hard-coded this to be enabled for Mainnet and disabled for other networks. This PR makes it configurable allowing is to:

• If we need to disable all private submission strategies, then we can still continue to function with the public mempool.
• If we eventually enable some additional private network submission for other networks (GChain, Polygon), then we can disable high-risk transactions to the public mempool without additional code changes

This PR is done in anticipation of The Merge™, where it is unclear whether or not Eden and Flashbots will continue to function for the first few epochs - so we need to be able to only submit to the public mempool in case of emergency.

Test Plan

Run without --disable-high-risk-public-mempool-transactions:

% cargo run -p solver
...
disable_high_risk_public_mempool_transactions: false
...

Run with --disable-high-risk-public-mempool-transactions:

% cargo run -p solver
...
disable_high_risk_public_mempool_transactions: false
...

Also, unit test that verifies filtering logic was added.

Release notes

• We need to set DISABLE_HIGH_RISK_PUBLIC_MEMPOOL_TRANSACTIONS=true environment variable for Mainnet and leave it unset for our other networks.