arrow

GH-43518: [Python][Packaging][CI] Drop Python 3.8 support (#43970)

### Rationale for this change

Python 3.8 is End of Support on 31st October 2023. We can drop support for pyarrow 18.0.0.
See: https://endoflife.date/python

### What changes are included in this PR?

Remove support for 3.8. Update minimum required Python version and update some CI jobs to use the minimum Python supported version

### Are these changes tested?

They will be tested via Archery

### Are there any user-facing changes?

Yes in terms of not supporting older versions of Python. This will be a breaking change for some users but not for the API itself

* GitHub Issue: #43518

Authored-by: Raúl Cumplido <raulcumplido@gmail.com>
Signed-off-by: Joris Van den Bossche <jorisvandenbossche@gmail.com>