feat: decode execute tx error

[sebastiendan]

Description

This PR follows topos-protocol/executor-service#20 in improving error handling between the Executor Service execute processor and the ERC20Messaging dApp frontend.

Fixes TOO-423

PR Checklist:

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added or updated tests that comprehensively prove my change is effective or that my feature works