Move Python version to 3.12

Currently, we rely on Python 3.8 due to historical use of OTB 7.4. With latest OTB versions, such as 9, it's really easy to use a newer versions by recompiling bindings.

It would be really nice to move to Python 3.12, which means:

• Having a OTB 9-Python 3.12 installed on CNES cluster (OTB Team should do that)
• Checking that our Python code, and rastertools works well with Python 3.12, install new environment
• Validate results.