Improvements to act-based testing

[xnyo]

#389 switches the smoke test system from using GitHub Actions directly to running act inside GitHub Actions. This allows us to write Go tests and run assertions on the workflows that are normally not possible or complicated to achieve via yaml files.

We can further improve act-based testing with some additional features:

• Parsing of GHA commands, annotations, outputs, etc, in order to run assertions on them
• Stronger assertions in the smoke tests (e.g.: CI output) rather than just asserting on success/failure
• Mock GCS for testing uploading to GCS (which is required for GCOM catalog publishing)
• Mock GCOM for testing catalog publishing steps
• Mock Vault access for testing accessing to Vault
• Mock Argo workflow triggers for testing CD
• Mock "Build and test" plugins in anything that doesn't test building or testing the plugin, to speed up act test runs ("Build and test" is the slowest job apart from Playwright)
• Introduce caching mechanism for the nektos/act docker image and act tooling docker volume to speed up execution