feat: ethereum execution specs workflow

[jhkimqd]

Description

• Add ethereum-execution-specs tests into the workflow
• PoS Compat Versions Check job now checks whether latest image versions are being used. This is only triggered if:
  • a PR is raised
  • and the PR includes changes in some pos related directory only
• Clean up Makefile to include helper scripts to update pos versions matrix + tests inventory

Example in CI -> some tests with invalid combinations are somewhat expected to fail, so we are mainly looking at whether the latest release tests are passing for sanity checks.