Send approve transaction on each deposit

[Stefan-Ethernal]

Description

This PR fixes sending approval transactions for RootERC20Predicate. Prior to this, it was sent only by the root chain contracts deployer, which allowed RootERC20Predicate to spend ERC20 tokens only on its behalf. Now approval transaction is being sent before each deposit, which is correct behavior, allowing arbitrary account to send deposit transaction and not only the root chain contracts deployer.

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

Manual tests

Please complete this section if you ran manual tests for this functionality, otherwise delete it

Documentation update

Please link the documentation update PR in this section if it's present, otherwise delete it

Additional comments

Please post additional comments in this section if you have them, otherwise delete it