EVM-749 Transaction pool Base Fee fix

[igorcrevar]

Description

Transaction pool base fee was populated only on Prepare call. This method was called from the block builder when the node is the proposer.

After these changes, every time a new block is inserted into the chain, the base fee in the transaction pool is recalculated. This recalculation is performed inside the processEvent method, which is called by the ResetWithHeaders.

Changes include

• Bugfix (non-breaking change that solves an issue)
• Hotfix (change that solves an urgent issue, and requires immediate attention)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)

Checklist

• I have assigned this PR to myself
• I have added at least 1 reviewer
• I have added the relevant labels
• I have updated the official documentation
• I have added sufficient documentation in code

Testing

• I have tested this code with the official test suite
• I have tested this code manually