Muttlib

Test that changelog has been modified in pipeline. This avoids merging MRs that have not updated the changelog.

Pinned `pandas` version and upgraded `pyarrow` to version 2.0.0.

CI/CD Pipelines updated, now [Merged Results](https://docs.gitlab.com/ee/ci/merge_request_pipelines/pipelines_for_merged_results) are activated.

Added to PR workflow explanation in CONTRIBUTING.md.

Closes 121 - Fix detached pipelines.

Modify string filter `format_in_clause`, now supporting string values.

- Add tests to `utils` module.

pylint setup final touches.

Closes 85 - pylint `forecast.py`