[Feature] for python modles, user can add their own log lines (including custom variables) and we will display them in the dbt CLI

### Is this your first time submitting a feature request?

- [x] I have read the [expectations for open source contributors](https://docs.getdbt.com/docs/contributing/oss-expectations)
- [x] I have searched the existing issues, and I could not find an existing issue for this feature
- [x] I am requesting a straightforward extension of existing dbt functionality, rather than a Big Idea better suited to a discussion

### Describe the feature

- for python modles, user can add their own log lines (including custom variables) and we will display them in the dbt CLI
- similar to what we support with Jinja {{ log() }}