Preparations for a 0.5.8 patch release following orix 0.9.0

[hakonanes]

Description of the change

Fixes breaking changes coming in orix 0.9.0 where e.g. Vector3d.azimuth is a NumPy array and not a Scalar (class in orix), which previously had to be accessed as Vector3d.azimuth.data.

Progress of the PR

• [n/a] Docstrings for all functions
• [x] Unit tests with pytest for all lines
• [n/a] Clean code style by running black via pre-commit
• [x] Update changelog
• [x] Release orix 0.9.0 on PyPI
• [x] Set minimal orix version to 0.9 in setup.py

For reviewers

• [ ] The PR title is short, concise, and will make sense 1 year later.
• [ ] New functions are imported in corresponding __init__.py.
• [ ] New features, API changes, and deprecations are mentioned in the unreleased section in CHANGELOG.rst.
• [ ] New contributors are added to .all-contributorsrc and the table is regenerated.

[hakonanes]

The code style has been updated per black 22.03 on the develop branch, so I won't update it here. Thus, I'll ignore that the code style check fails.