EVM-568 Increase MaxBlockBacklog for block tracker

[igorcrevar]

Description

Part of the event tracker is the block tracker, which fetches blocks from provided JSON RPC endpoint. In order to determine if there are reorgs happening, there is a MaxBlockBacklog parameter. It turned out that default value of 10 blocks is not big enough.

The solution proposal is to initialize the MaxBlockBacklog parameter as 2*NumBlockConfirmations (or consider putting even more).

BlockTracker creation/initialization is moved to tracker/event_tracker.go. That way we have much more options when configuring blocktracker

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