Better error messages and documentation for E2E / exec.yaml

I took the exec/E2E yaml files from the generic example and tried to adapt to a given project. it would be nice if the error message or some docs existed about how to properly put those pieces together.

error message:

```
`test failure` failure:
max timed out reached for test: 'test failure' with errors: 1 error occurred:
* max retries exceeded

`test success` failure:
missing assertion for stage DynamoDb terraform_state_locking table management

# tried also using that pipeline name instead of "Stage 1" and got similar failure.
```

Start with the generic example and the exec/E2E YAML files, then reproduce the reported test failure using the shown configuration. Document how the pieces fit together and clarify the missing assertion and timeout errors so users can tell when the configuration is correct.

Written by the indexing model from the issue text.