[Github] Max fee per gas issue

[begmaroman]

Description

eth_call and eth_estimateGas endpoints are simulating transaction execution.
Transaction execution process has tx price so price-related fields should be provided in order to get transaction executed.
Currently, those two endpoints use a transaction object with an empty tx price so the simulation immediately fails.

This PR introduces a logic to apply gas price if a zero value is provided.

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