Simplify tokens amount providing in e2e tests

[Stefan-Ethernal]

Description

This PR uses helper functions from ethgo, which enables tests to be more verbose, by using ethgo.Ether and ethgo.Gwei, instead of specifying huge strings representing token amounts, which are hard for understanding.

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)

Breaking changes

Please complete this section if any breaking changes have been made, otherwise delete it

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

[vcastellm]

LGTM