local.conf: Enable pressure monitoring

The BB_PRESSURE_MAX_CPU can be set to monitor /proc/pressure/cpu
when scheduling new tasks. I start with a relativly high value, I'm
currently not quite sure how to find out the correct one.

For the general feature
see:

https://www.linux-magazin.de/ausgaben/2020/08/psi
https://www.kernel.org/doc/html/latest/accounting/psi.html
https://docs.yoctoproject.org/bitbake/2.6/bitbake-user-manual/bitbake-user-manual-ref-variables.html#term-BB_PRESSURE_MAX_CPU

The general algorithm is to take the 'total=' number's increment in the
last second and compare it with the threshold.
The bitbake user manual suggests 500, but I've hardly seen such low
values, that's why I'm starting with a much higher one.

The actual usage of the limit is implemeted in
https://git.seco.com/seco-ne/3rd-party/yocto/poky/-/blob/seconorth/kirkstone/bitbake/lib/bb/runqueue.py?ref_type=heads#L193
Some additional debug messages might be added here to monitor, when the
limit is hit.