Add 'dbt-cloud audit-log get' command

[stumelius]

Description & motivation

Audit logs are available for Enterprise accounts only so we have no way of testing this in CI.

Checklist

• [x] I have written unit tests for new features (e.g., a new command test case in conftest.py)
• [x] I have written integration tests for new features (e.g., a new step in the CI workflow)
• [x] I have added descriptions to new commands and arguments
• [x] I have updated the README.md (if applicable)