Enable CONFIG_PSI in the default kernel

**Is your feature request related to a problem? Please describe.**
The current default WSL kernel is built with CONFIG_PSI unset, which means the [process stall information](https://docs.kernel.org/accounting/psi.html) metrics are not collected or exposed, so things that rely on those (notably systemd-oomd, a userspace early-OOM service) do not work.

**Describe the solution you'd like**
CONFIG_PSI=y is enabled in the kernel.

**Describe alternatives you've considered**
Leave things as they are.

**Additional context**
While systemd-oomd may seem unhelpful, as the VM's memory is already limited, it does help prevent the VM itself from locking up when under heavy memory pressure, forcing the user to kill the entire VM and possibly lose data.

Locate the default WSL kernel configuration and inspect how kernel options are defined. Confirm whether CONFIG_PSI is unset, then enable it as requested and verify that the resulting configuration exposes process stall information for systemd-oomd.

Written by the indexing model from the issue text.