generators: change TimeoutSec=0 to TimeoutSec=infinity

generators: change TimeoutSec=0 to TimeoutSec=infinity

With these settings we intend to turn off timeouts for possibly
interactive/slow commands. The officially documented way to turn off the
time-outs is to setting them to infinity. So far we set them to zero
here though.

This lead to some confusiong, for example #18224. Let's fix this by
uniformly spelling out TimeoutSec=infinity.

This doesn't change behaviour. It just makes our generated files match
what we document, without relying on historic compat support.

Fixes: #18224