Introduce v3.12 python runtime in serverless

[kwiatekus]

Description

Add version `v3.12 to supported python serverless runtimes.

AC

• new runtime is selectable from kyma dashboard
• python 3.9 stays the default
• new runtime is usable from kyma cli
• update documentation

Reasons

Keep up with Python versions

Attachments

could be helpful (for reference.. but its probably not 1:1 after modularization) - kyma-project/kyma#16765

[halamix2]

Python 3.9 commits for reference

• Support Python v3.9.5 as serverless runtime kyma#11299
• Add Python39 runtime kyma#11498
• Add python39 runtime busola#239

[halamix2]

For the next task of deprecating 3.9: don't forget to update Python version in https://github.com/kyma-project/private-fn-for-e2e-serverless-tests

[kwiatekus]

When using fresh kyma cli from main I cannot initialize python 312

kyma init function --runtime python312 --name python                                                                                               
X Generating project structure (8ms)
Error: unsupported runtime