Drop support for Python 3.8

[soxofaan]

Python 3.8 reached end of life October last year (2024-10-07).

This ticket is to collect and cross-reference reasons for dropping support.

Previous editions:

• Drop support for Python 3.7 #578
• Drop support for python 3.6 #460
• Drop support for Python 3.5? #210

[soxofaan]

big reason we can not drop it yet: most deployments of openeo geopyspark driver are still bound to 3.8

• [EPIC] multi-image/version pipelines openeo-geotrellis-kubernetes#25

[soxofaan]

problem in #714: geopandas dropped python 3.8 support in 0.14.0 (Sept 2023)

[soxofaan]

another possible problem as we are depending more and more on stac/pystac: pystac dropped python 3.8 support in version 1.9.0 (2023-10-23)