Features:
+* introduce a .microcode PE section for sd-stub which we'll pass as first initrd
+ to the kernel which will then upload it to the CPU. This should be distinct
+ from .initrd to guarantee right ordering. also, and maybe more importantly
+ support .microcode in PE add-ons, so that a microcode update can be shipped
+ indepdendently of any kernel.
+
+* add clean mechanism concept for passing env/creds from initrd to host on
+ switch root, so that cloud-init and similar have a clean, sane method to pass
+ along the stuff they picked up, without patching any dirs. Maybe add
+ SwitchRootEx() as new bus call that takes these as argument. When adding
+ SwitchRootEx() we should maybe also add a flags param that allows disabling
+ and enabling whether serialization is requested during switch root.
+
+* add proper .osrel matching for PE addons. i.e. refuse applying an addon
+ intended for a different OS. Take inspiration from how confext/sysext are
+ matched against OS.
+
* use different sbat for sd-boot and sd-stub (so that people can revoke one
without the other)