Set better defaults in PythonPackage

[Flamefire]

We tend to set

download_dep_fail = True
use_pip = True
sanity_pip_check = True

for all PythonPackage ECs nowadays and pip should be the default to install PythonPackages as well as the sanity check and download_dep_fail.

Hence for EasyBuild 5.0 I propose to set this as the default which is a potentially breaking change for ECs not updated but likely to work for most packages anyway.

@boegel if agreed please add this to the 5.0 milestone

[Flamefire]

Pinging in here after discovering an issue caused by not using pip: #2389

[boegel]

This will be fixed by #3022